Ecological speciation

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Ecological_speciation 

 

Three-spined stickleback fish have been a frequently studied species in ecological speciation.

Ecological speciation is a form of speciation arising from reproductive isolation that occurs due to an ecological factor that reduces or eliminates gene flow between two populations of a species. Ecological factors can include changes in the environmental conditions in which a species experiences, such as behavioral changes involving predation, predator avoidance, pollinator attraction, and foraging; as well as changes in mate choice due to sexual selection or communication systems. Ecologically-driven reproductive isolation under divergent natural selection leads to the formation of new species. This has been documented in many cases in nature and has been a major focus of research on speciation for the past few decades.

Ecological speciation has been defined in various ways to identify it as distinct from non-ecological forms of speciation. The evolutionary biologist Dolph Schluter defines it as, "...the evolution of reproductive isolation between populations or subsets of a single population by adaptation to different environments or ecological niches", while others have added that divergent natural selection is the driving force. The key difference between ecological speciation and other kinds of speciation, is that it is triggered by divergent natural selection among different habitats; as opposed to other kinds of speciation processes, like random genetic drift, the fixation of incompatible mutations in populations experiencing similar selective pressures, or various forms of sexual selection not involving selection on ecologically relevant traits. Ecological speciation can occur either in allopatry, sympatry, or parapatry. The only requirement being that speciation occurs as a result of adaptation to different ecological or micro-ecological conditions.

Ecological speciation can occur pre-zygotically (barriers to reproduction that occur before the formation of a zygote) or post-zygotically (barriers to reproduction that occur after the formation of a zygote). Examples of pre-zygotic isolation include habitat isolation, isolation via pollinator-pollination systems, and temporal isolation. Examples of post-zygotic isolation involve genetic incompatibilities of hybrids, low fitness hybrids, and sexual selection against hybrids.

Some debate exists over the framework concerning the delineation of whether a speciation event is ecological or nonecological. "The pervasive effect of selection suggests that adaptive evolution and speciation are inseparable, casting doubt on whether speciation is ever nonecological". However, there are numerous examples of closely related, ecologically similar species (e.g., Albinaria land snails on islands in the Mediterranean, Batrachoseps salamanders from California, and certain crickets and damselflies), which is a pattern consistent with the possibility of nonecological speciation.

Ecological causes of divergent selection

Divergent selection is key to the occurrence of ecological speciation. Three ecological causes of divergent selection have been identified: differences in environmental conditions, ecological interactions, and sexual selection.

Two types of experimental tests of ecological speciation caused by divergent environments.
Experiment 1: a speciation event predicted to have occurred due to an ecologically-based divergent factor giving rise to two new species (1a). The experiment produces viable and fertile hybrid offspring and places them in isolated settings that match their parental environments (1b). The experiment predicts that, "reproductive isolation should then evolve in correlation with environment, building [increasing] between populations in different environments and being absent between laboratory and natural populations from similar environments."
Experiment 2: a peripatric speciation event between a mainland species and an isolated endemic population occurs (2a). A laboratory setting replicates the mainland environmental conditions thought to have driven speciation and a mainland population is placed within it. The experiment predicts that the transplant will show evidence of isolation that matches that of the island endemic (2b).

• Differences in environmental conditions as a prerequisite to speciation is incontrovertibly the most studied. Predation, resource availability (food abundance), climatic conditions, and the structure of a habitat are some of the examples that can differ and give rise to divergent selection. Despite being one of the most studied factors in ecological speciation, many aspects are still less understood such as how prevalent the process is in nature as well as the origin of barriers for post-zygotic isolation (as opposed to the much easier detectable pre-zygotic barriers). Laboratory experiments involving single-environmental differences are limited and have often not tracked the traits involved in isolation. Studies in nature have focused on a variety of environmental factors such as predation-caused divergent selection; however, little has been studied in regards to pathogens or parasites.
• Ecological interactions can drive divergent selection between populations in sympatry. Examples of these interactions can be intraspecific (between the same species) and interspecific (between different species) competition or relationships such as those of ecological facilitation). Interspecific competition in particular has support from experiments; however it is unknown if it can give rise to reproductive isolation despite driving divergent selection. Reinforcement (the strengthening of isolation by selection favoring the mating of members of their own populations due to reduced fitness of hybrids) is considered to be a form of, or involved in, ecological speciation. Though, debate exists as to how to determine ultimate causes since reinforcement can complete the speciation process regardless of how it originated. Further, character displacement can have the same effect.
• Sexual selection can play a role in ecological speciation as the recognition of mates is central to reproductive isolation — that is, if a species cannot recognize its potential mates, the flow of genes is suspended. Despite its role, only two types of sexual selection can be implicated in ecological speciation: the spatial variation in secondary sexual traits (sexual traits that arise specifically at sexual maturity) or communication and mating systems.) This restriction is based on the fact that they produce diverging environments in which selection can act. For example, isolation will increase between two populations where there is a mismatch between signals (such as the feather display of a male bird) and the preferences (such as the sexual preferences of a female bird). This pattern has been detected in stickleback fish.

A summary of the various types of ecological isolation and its drivers.

Reproductive isolation type	Pre-zygotic or post-zygotic	Ecological cause of selection
		Divergent environments	Ecological interactions	Sexual selection	Reinforcement
Habitat	Pre	✓	✓		✓
Sexual/Pollinator	Pre	✓	✓	✓	✓
Temporal	Pre	✓	✓		✓
Selection against migrants	Pre	✓	✓		✓
Post-mating	Pre	✓	✓	✓	✓
Selection against hybrids	Post	✓	✓	✓	✓
Ecologically-independent	Post	✓	✓	✓	✓
Ecologically-dependent	Post	✓	✓

Types of reproductive isolation

Habitat isolation

Micro-spatial and macro-spatial isolation differs by the feature of the habitat; whether it is patchy (such as fragmented forest interspersed with grassland) or a gradient (such as forest transitioning gradually into shrub or grassland.

Populations of a species can become spatially isolated due to preferences for separate habitats. The separation decreases the chance of mating to occur between the two populations, inhibiting gene flow, and promoting pre-zygotic isolation to lead to complete speciation. Habitat isolation is not equivalent to a geographic barrier like that of allopatric speciation. Instead, it is based on genetic differences, where one species is unable to exploit a different environment, resulting from fitness advantages, fitness disadvantages, or resource competition.

Jerry Coyne and H. Allen Orr posit two different forms of habitat isolation: microspatial habitat isolation (where matings between two species are reduced by preferences or adaptations to ecologically differing areas, despite occupying the same generalized area) and macrospatial habitat isolation (defined by fully allopatric habitats that inhibit gene flow.) Identification of both forms of habitat isolation in nature is difficult due to the effects of geography. Measuring microspatial isolation demands several factors:

• the spatial separation of different species' members is greater than those of members of the same species
• during simultaneous breeding periods, the spatial separation reduces gene flow
• decreased gene flow is directly the result of decreased mating
• genetic differences correspond to the spatial separation

Allopatric distributions pose several problems for detecting true habitat isolation in that different habitats of two allopatrically isolated species does not imply ecologically caused speciation. Alternative explanations could account for the patterns:

• species differences may be caused by geographic isolation
• the species may or may not occupy different habitats if they existed in sympatry
• in cases of similar habitats in allopatry, species may be adapted to unknown ecological factors
• if the species existed in sympatry, competition may drive habitat segregation that would be undetectable in allopatry

These issues (with both micro- and macro-spatial isolation) can be overcome by field or laboratory experiments such as transplantation of individuals into opposite habitats (though this can prove difficult if individuals are not completely unfit for the imposed habitat). Habitat isolation can be measured for a species pair (${\displaystyle a}$ and ${\displaystyle b}$) during a breeding period by:

${\displaystyle 1-{\frac {p_{ab}}{2p_{a}p_{b}}}}$

Here, ${\displaystyle p_{ab}}$ is the proportion of encounters between matings that involve partners of a different species that are observed. ${\displaystyle p_{a}}$ is the proportion of total individuals of species ${\displaystyle a}$. ${\displaystyle p_{b}}$ is the proportion of total individuals of species ${\displaystyle b}$. The expected proportion of mating encounters between different species if mating is random is denoted by ${\displaystyle 2p_{a}p_{b}}$. A statistic of ${\displaystyle 1}$ indicates no mating encounters of different species where ${\displaystyle 0}$ indicates random mating of different species.

Geography

Ecological speciation caused by habitat isolation can occur in any geographic sense, that is, either allopatrically, parapatrically, or sympatrically. Speciation arising by habitat isolation in allopatry (and parapatry) is straightforward in that reduced gene flow between two populations acquire adaptations that fit the ecological conditions of their habitat. The adaptations are reinforced by selection and, in many cases such as with animals, are reinforced by behavioral preferences (e.g. in birds that prefer specific vocalizations). A classic example of habitat isolation occurring in allopatry is that of host-specific cospeciation such as in the pocket gophers and their host chewing lice or in the fig wasp-fig tree relationship and the yucca-yucca moth relationship—examples of ecological speciation caused by pollinator isolation. In sympatry, the scenario is more complex, as gene flow may not be reduced enough to permit speciation. It is thought that selection for niche divergence can drive the process. In addition, if sympatry results from the secondary contact of two previously separated populations, the process of reinforcement, the selection against unfit hybrids between the two populations, may drive their complete speciation. Competition for resources may also play a role.

The western American sagebrush Artemisia tridentata

Habitat isolation is a significant impediment to gene flow and is exhibited by the common observation that plants and animals are often spatially separated in relation to their adaptations. Numerous field studies, transplantation and removal experiments, and laboratory studies have been conducted to understand the nature of speciation caused by habitat isolation. Horkelia fusca, for example, grows on California slopes and meadows above 4500 feet, where its closet relatives H. californica and H. cuneata grow below 3200 feet in coastal habitats. When species are transplanted to alternate habitats, their viability is reduced, indicating that gene flow between the populations is unlikely. Similar patterns have been found with Artemisia tridentata tridentata and A. tridentata subsp. vaseyana in Utah, where hybrid zones exists between altitudinal populations, and transplant experiments reduce the fitness of the subspecies.

Speciation by habitat isolation has also been studied in serpentine leaf miner flies, ladybird beetles (Epilachna), goldenrod gall flies, Rhagoletis pomonella, leaf beetles, and pea aphids.

Sexual isolation

Ecological speciation due to sexual isolation results from differing environmental conditions that modify communication systems or mate choice patterns over time. Examples abound in nature. The coastal snail species Littorina saxatilis has been a focus of research as two ecotypes residing at different shore levels exhibit reproductive isolation as a result of mate choice regarding the body size differences of the ecotype. Both marine and freshwater stickleback fish have shown strong evidence of having speciated this way. Evidence is also found in Neochlamisus bebbianae leaf beetles, Timema cristinae walking-stick insects, and in the butterfly species Heliconius melpomene and H. cydno which are thought to have diverged recently due to assortive mating being enhanced where the species populations meet in sympatry.

Pollinator isolation

Angiosperms (flowering plants) require some form of pollination—many of which require another animal to transfer pollen from one flower to another. Biotic pollination methods require pollinators such as insects (e.g. bees, butterflies, moths, wasps, beetles, and other invertebrates), birds, bats, and other vertebrate species. Because of this evolutionary relationship between pollinators and pollen-producing plants, plants and animals become mutually dependent on each other—the pollinator receives food in the form of nectar and the flower gains the ability to propagate its genes.

In the event that an animal uses a different pollination source, plants can become reproductively isolated. Pollinator isolation is a specific form of sexual isolation. The botanist Verne Grant distinguished between two types of pollinator isolation: mechanical isolation and ethological isolation.

Mechanical pollinator isolation

Pollen from each species Catasetum saccatum (I) and Catasetum discolor (II) attach to the dorsal and ventral parts of Eulaema cingulata (◊) respectively.

Mechanical isolation results from anatomical differences of a flower or pollinator preventing pollination from occurring. For example, in the bee Eulaema cingulata, pollen from Catasetum discolor and C. saccatum is attached to different parts of the body (ventrally and dorsally respectively). Another example is with elephant's head and little elephant's head plants. They are not known to hybridize despite growing in the same region and being pollinated by the same bee species. Pollen is attached to different parts of the bee rendering the flowers isolated. Mechanical isolation also includes pollinators who are unable to pollinate due to physical inabilities. Nectar spur length, for example, could vary in size in a flower species resulting in pollination from different lepidopteran species due to the lengths preventing body contact with the flower's pollen.

Ethological pollinator isolation

Hypothetical flower visitation by various pollinators. Overlap exists, though some species are exclusive pollinators illustrating how pollinator isolation can be detected in natural or laboratory settings.

Ethological isolation is based on behavioral traits of pollinators that prefer different morphological characteristics of a flower either genetically or through learned behavior. These characteristics could be the overall shape and structure, color, type of nectar, or smell of the flower. In some cases, mutualisms evolve between a pollinator and its host, cospeciating with near-congruent, parallel phylogenies. That is, the dependent relationship results in closely identical evolutionary trees indicating that speciation events and the rate of speciation is identical. Examples are found in fig wasps and their fig hosts, with each fig wasp species pollinating a specific fig species. The yucca and yucca moth exhibit this same pattern.

Transition of hybrid forms between the white A. pubescens and the red-and-yellow A. formosa

 

A hypothetical example of incipient speciation represented by differential geographic occurrence and nectar volume. The differing morphologies of the flower species results from selection towards traits that are more attractive to their available pollinators. The hummingbird has a greater affinity for red flowers and more nectar. The bee is attracted to purple flowers and demands less nectar. Hybrid flowers exist where ranges meet but are less attractive to pollinators thereby occurring less frequently.

In a striking case, two closely related flowering plants (Erythranthe lewisii and E. cardinalis) have speciated due to pollinator isolation in complete sympatry (speciation occurring without any physical, geographic isolation). E. lewisii has changed significantly from its sister species in that its evolved pink flowers, broad petals, shorter stamens (the pollen-producing part of the plant), and a lower volume of nectar. It is entirely pollinated by bees with almost no crossing in nature. E. cardinalis is pollinated by hummingbirds and exhibits red, tube-shaped flowers, larger stamens, and a lot of nectar. It is thought that nectar volume as well as a genetic component (an allele substitution that controls color variation) maintains isolation. A similar pattern has been found in Aquilegia pubescens and A. formosa. In this species pair, A. pubescens is pollinated by hawkmoths while A. formosa is pollinated by hummingbirds. Unlike in Erythranthe, these species reside in different habitats but exhibit hybrid forms where their habitats overlap; though they remain separate species suggesting that the hybrid flowers may be less attractive to their pollinator hosts.

Geography

Four geographic-based scenarios involving pollinator isolation are known to occur:

• The most common framework for pollinator isolation in a geographic context implies that floral trait divergence occurs as a result of geographic isolation (allopatrically). From there, a population has the potential to encounter different pollinators ultimately resulting in selection favoring traits to attract the pollinators and achieve reproductive success.
• Another scenario involves an initial allopatric stage, wherein secondary contact occurs at a variable level of reproductive isolation—high isolation is effectively allopatric speciation whereas low isolation is effectively sympatric. This "two-stage" model is indicated in the three-spined sticklebacks as well as the apple maggot fly and its apple hosts.
• A pollinator can change preferences due to its own evolution driving selection to favor traits that align with the pollinators changed preferences.
• There exists the possibility that when two populations become isolated geographically, a plant or pollinator could go extinct in one of the populations driving selection to favor different traits.

A species population of pink-petal flowers becomes isolated in allopatry or parapatry. Novel pollinators drive the selection of new traits (purple petals) in the isolated populations eventually leading to speciation of the flower populations. It is possible for the same pollinator to drive the selection of new flower traits as long as the proportions of pollinators differ enough.

Jerry Coyne and H. Allen Orr contend that any scenario of pollinator isolation in allopatry demands that incipient stages should be found in different populations. This has been observed to varying degrees in several species-pollinator pairs. Flower size of Raphanus sativus (in this case, wild radish in 32 California populations) has been found to differ in accordance with larger honeybee pollinators. Polemonium viscosum flowers have been found to increase in size along an alpine gradient in the Colorado Rocky Mountains as flies pollinate at the timberline whereas bumblebees pollinate at higher elevations. A similar pattern involving the timing in which hawkmoths (Hyles lineata) are active is documented in three subspecies of Aquilegia coerulea, the Rocky Mountain columbine found across the western United States.

The most notable example according to Coyne and Orr is that of the African orchid subspecies Satyrium hallackii hallackii and Satyrium hallackii ocellatum. The latter is pollinated by moths and exhibits long nectar spurs that correlate with the moth's proboscis. Unlike the inland, grassland habitat of subspecies hallackii, ocellatum resides in coastal populations and has short spurs that correlate with its primary carpenter bee pollinator. The moths are unable to find suitable nest sites in coastal habitats while the bees are unable inland. This pattern separates the pollinator populations but does not separate the orchid population driving selection to favor flower differences that better-match the local pollinators. A similar pattern has been detected in studies of the Disa draconis complex in South Africa.

Temporal isolation (allochronic speciation)

Main article: Allochronic speciation

 

Breeding seasons of three populations of a species shift over time eventually causing the isolation of their genes from the other populations. This reproductive isolation can lead to speciation.

Temporal isolation is based on the reduction of gene flow between two populations due to different breeding times (phenology). It is also referred to as allochronic isolation, allochronic speciation, or allochrony. In plants, breeding in regards to time could involve the receptivity of stigma to accepting sperm, periods of pollen release (such as in conifer trees where cones disperse pollen via wind), or overall timing of flowering. In contrast, animals often have mating periods or seasons (and many aquatic animals have spawning times). Migratory patterns have also been implicated in allochronic speciation.

For allochronic speciation to be considered to have actually occurred, the model necessitates three major requirements:

1. Phylogenetic analysis indicates the incipient species are sister taxa
2. Breeding timing is genetically-based (heritable to offspring)
3. The source of divergence is explicitly allochrony and not the result of reinforcement or other mechanisms

Allochrony is thought to evolve more easily the greater the heritability of reproductive timing—that is, the greater the link between genes and the timing of reproduction—the more likely speciation will occur. Temporal isolation is unique in that it can be explicitly sympatric as well as non-genetic; however genetic factors must be involved for isolation to lead to complete reproductive isolation and subsequent speciation. Speciation by allochrony is known to occur in three time frames: yearly (e.g. periodic cicadas emerging over decades or multi-decadal bamboo flowerings), seasonal (organisms that breed during times of the year such as winter or summer), and daily (e.g. daily spawning times of corals). The table list below summarizes a number of studies considered to be strong or compelling examples of allochronic speciation occurring in nature.

Table of known or likely allochronic speciation events.

Species	Description
Acropora spp.	Japanese corals found to be reproductively isolated by the timing of their spawning.
Montastraea annularis, M. faveolata, and M. franksi	Three related species of coral that have speciated due to the timing of their spawning.
Oncorhynchus nerka	Yearly breeding runs of Sockeye salmon occur during two periods in the year (late and early) have caused genetic isolation of incipient populations. Salmon breeding is known to be genetic but no specific genes are known for this species.
Thaumetopoea pityocampa	Codominance in genes is associated with the emergence time for larval stages of this moth species. Winter and summer larval populations are in the process of speciating.
Inurois punctigera	Breeding is prevented in areas where mid-winter temperatures are unsuitable for the moth species. This has given rise to late and early populations.
Pemphigus populi-transversus and P. obesinymphae	The gall-forming aphids produce galls on different leaves of the same host tree species. P. populi-transversus forms galls on early spring leaves while P. obesinymphae forms them on leaves in the summer. This has led to full reproductive isolation.
Asphondylia spp.	Three midge species infect the stems of Larrea tridentata, A. auripila in summer, A. resinosa in winter, and A. foliosa in spring.
Acropora samoensis	Sympatric species populations of coral spawn separately in the fall and spring with spawning being a heritable, likely involving the PaxC gene.
Cellana spp.	Inhabiting different depths within centimeters, the limpets have become reproductively isolated likely due to a combination of parapatric speciation and spawn cues (e.g. spawning according to water level.
Hydrobates spp.	The petrels group has reproductively isolated (in the Azores) and incipient species (other archipelagos) caused by cool and warm breeding seasons.
Howea belmoreana and H. forsteriana	Genetically controlled flowering times have caused (in conjunction with differing soil pH levels) the reproductive isolation of two palm species on Lord Howe Island.
Erysiphe necator	Exhibits evidence of isolation due to temporal differences of its host species Vitis vinifera.
Oncorhynchus gorbuscha	Even and odd two-year life cycles in conjunction with seasonal breeding runs of pink salmon has driven genetic differentiation between the two populations.
Magicicada spp.	Groups of 13- and 17-year life cycle species pairs (seven species total) of cicada emerge to reproduce separated by large time frames between breading seasons. Only every 221 years do the 13 and 17 year cycles align where both pairs emerge simultaneously.
Antitrogus parvulus	Two beetle cohorts express genetic differentiation from life cycles separated by two-year intervals.
Oeneis melissa semidea	Two-year life cycles of the butterfly species breeding groups have caused genetic differentiation.
Bambusoideae	Bamboo under go semelparous reproduction where they live for years before mass-flowering at once. This can happen in different years and different locations. Allochronic patches are thought to have driven the diversification of global bamboo species.

Other pre-zygotic forms of ecological isolation

Selection against migrants, or immigrant inviability, is hypothesized to be a form of ecological isolation. This type of speciation involves the low survival rates of migrants between populations because of their lack of adaptations to non-native habitats. There is little understanding the relationship between post-mating, pre-zygotic isolation and ecology. Post-mating isolation occurs between the process of copulation (or pollination) and fertilization—also known as gametic isolation. Some studies involving gametic isolation in Drosophila fruit flies, ground crickets, and Helianthus plants suggest that there may be a role in ecology; however it is undetermined.

Post-zygotic forms of ecological isolation

Three forms of ecologically-based post-zygotic isolation:
1. Ecologically-independent post-zygotic isolation.
2. Ecologically-dependent post-zygotic isolation.
3. Selection against hybrids.

Ecologically-independent post-zygotic isolation arises out of genetic incompatibilities between two hybrid individuals of a species. It is thought that in some cases, hybrids have lower fitness especially based on the environment in which they reside. For example, in extreme environments with limited ecological niches to exploit, high fitness is necessitated, whereas if an environment has lots of niches, lower fit individuals may be able to survive for longer. Some studies indicate that these incompatibilities are a cause of ecological speciation because they can evolve quickly through divergent selection.

Ecologically-dependent post-zygotic isolation results from the reduce hybrid of fitness due to its position in an ecological niche— that is, parental species occupy slightly different niches, but their hybrid offspring end up requiring a niche that is a blend between the two of which does not typically exist (in regard to a fitness landscape). This has been detected in populations of sticklebacks (Gasterosteus aculeatus), water-lily beetles (Galerucella nymphaeae), pea aphids, and tephritid flies (Eurosta solidaginis).

Selection against hybrids can sometimes (it is possible that non-ecological speciation can be attributed) be considered a form of ecological isolation if it originates from an ecological mechanism. For example, the hybrid offspring may be seen as "less attractive" to mates due to intermediate sexual displays or differences in sexual communication. The end result is that the genes of each parental population are unable to intermix as they are carried by a hybrid who is unlikely to reproduce. This pattern of sexual selection against hybrid offspring has been found in Heliconius butterflies. The two species H. cydno and H. melpomene are distributed sympatrically in South America and hybridize infrequently. When they do hybridize, the species shows strong assortive mating due to the mimicry-evolved color pattern that hybrid offspring have an intermediate of. Similar patterns have been found in lacewings migrating patterns of Sylvia atricapilla bird populations, wolf spiders (Schizocosa ocreata and S. rovneri) and their courtship behaviors, sympatric benthic and limnetic sticklebacks (the Gasterosteus aculeatus complex), and the Panamanian butterflies Anartia fatima and A. amathea. Flowers involving pollinator discrimination against hybrids have shown this pattern as well, in monkey flowers (Erythranthe lewisii and Erythranthe cardinalis) and in two species of the Louisiana iris group, Iris fulva and I. hexagona.

Synthetic diamond

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Synthetic_diamond 

 

Lab grown diamonds of various colors grown by the high-pressure high-temperature technique

Lab grown diamond (also called laboratory-grown, laboratory-created, man-made, artisan created, or cultured diamond) is diamond that is produced in a controlled technological process (in contrast to naturally formed diamond, which is created through geological processes and obtained by mining). Unlike diamond simulants (imitations of diamond made of superficially-similar non-diamond materials), synthetic diamonds are composed of the same material as naturally formed diamonds – pure carbon crystallized in an isotropic 3D form – and share identical chemical and physical properties.

Numerous claims of diamond synthesis were reported between 1879 and 1928; most of these attempts were carefully analyzed but none was confirmed. In the 1940s, systematic research of diamond creation began in the United States, Sweden and the Soviet Union, which culminated in the first reproducible synthesis in 1953. Further research activity yielded the discoveries of HPHT diamond and CVD diamond, named for their production method (high-pressure high-temperature and chemical vapor deposition, respectively). These two processes still dominate synthetic diamond production. A third method in which nanometer-sized diamond grains are created in a detonation of carbon-containing explosives, known as detonation synthesis, entered the market in the late 1990s. A fourth method, treating graphite with high-power ultrasound, has been demonstrated in the laboratory, but currently has no commercial application.

The properties of man-made diamond depend on the manufacturing process. Some synthetic diamonds have properties such as hardness, thermal conductivity and electron mobility that are superior to those of most naturally formed diamonds. Synthetic diamond is widely used in abrasives, in cutting and polishing tools and in heat sinks. Electronic applications of synthetic diamond are being developed, including high-power switches at power stations, high-frequency field-effect transistors and light-emitting diodes. Synthetic diamond detectors of ultraviolet (UV) light or high-energy particles are used at high-energy research facilities and are available commercially. Due to its unique combination of thermal and chemical stability, low thermal expansion and high optical transparency in a wide spectral range, synthetic diamond is becoming the most popular material for optical windows in high-power CO
₂ lasers and gyrotrons. It is estimated that 98% of industrial-grade diamond demand is supplied with synthetic diamonds.

Both CVD and HPHT diamonds can be cut into gems and various colors can be produced: clear white, yellow, brown, blue, green and orange. The advent of synthetic gems on the market created major concerns in the diamond trading business, as a result of which special spectroscopic devices and techniques have been developed to distinguish synthetic and natural diamonds.

History

Moissan trying to create synthetic diamonds using an electric arc furnace

After the 1797 discovery that diamond was pure carbon, many attempts were made to convert various cheap forms of carbon into diamond. The earliest successes were reported by James Ballantyne Hannay in 1879 and by Ferdinand Frédéric Henri Moissan in 1893. Their method involved heating charcoal at up to 3,500 °C (6,330 °F) with iron inside a carbon crucible in a furnace. Whereas Hannay used a flame-heated tube, Moissan applied his newly developed electric arc furnace, in which an electric arc was struck between carbon rods inside blocks of lime. The molten iron was then rapidly cooled by immersion in water. The contraction generated by the cooling supposedly produced the high pressure required to transform graphite into diamond. Moissan published his work in a series of articles in the 1890s.

Many other scientists tried to replicate his experiments. Sir William Crookes claimed success in 1909. Otto Ruff claimed in 1917 to have produced diamonds up to 7 mm (0.28 in) in diameter, but later retracted his statement. In 1926, Dr. J. Willard Hershey of McPherson College replicated Moissan's and Ruff's experiments, producing a synthetic diamond; that specimen is on display at the McPherson Museum in Kansas. Despite the claims of Moissan, Ruff, and Hershey, other experimenters were unable to reproduce their synthesis.

The most definitive replication attempts were performed by Sir Charles Algernon Parsons. A prominent scientist and engineer known for his invention of the steam turbine, he spent about 40 years (1882–1922) and a considerable part of his fortune trying to reproduce the experiments of Moissan and Hannay, but also adapted processes of his own. Parsons was known for his painstakingly accurate approach and methodical record keeping; all his resulting samples were preserved for further analysis by an independent party. He wrote a number of articles—some of the earliest on HPHT diamond—in which he claimed to have produced small diamonds. However, in 1928, he authorized Dr. C. H. Desch to publish an article in which he stated his belief that no synthetic diamonds (including those of Moissan and others) had been produced up to that date. He suggested that most diamonds that had been produced up to that point were likely synthetic spinel.

ASEA

First synthetic diamonds by ASEA 1953

The first known (but initially not reported) diamond synthesis was achieved on February 16, 1953 in Stockholm by ASEA (Allmänna Svenska Elektriska Aktiebolaget), Sweden's major electrical equipment manufacturing company. Starting in 1942, ASEA employed a team of five scientists and engineers as part of a top-secret diamond-making project code-named QUINTUS. The team used a bulky split-sphere apparatus designed by Baltzar von Platen and Anders Kämpe. Pressure was maintained within the device at an estimated 8.4 GPa (1,220,000 psi) and a temperature of 2,400 °C (4,350 °F) for an hour. A few small diamonds were produced, but not of gem quality or size.

Due to questions on the patent process and the reasonable belief that no other serious diamond synthesis research occurred globally, the board of ASEA opted against publicity and patent applications. Thus the announcement of the ASEA results occurred shortly after the GE press conference of February 15, 1955.

GE diamond project

A belt press produced in the 1980s by KOBELCO

In 1941, an agreement was made between the General Electric (GE), Norton and Carborundum companies to further develop diamond synthesis. They were able to heat carbon to about 3,000 °C (5,430 °F) under a pressure of 3.5 gigapascals (510,000 psi) for a few seconds. Soon thereafter, the Second World War interrupted the project. It was resumed in 1951 at the Schenectady Laboratories of GE, and a high-pressure diamond group was formed with Francis P. Bundy and H. M. Strong. Tracy Hall and others joined the project later.

The Schenectady group improved on the anvils designed by Percy Bridgman, who received a Nobel Prize in Physics for his work in 1946. Bundy and Strong made the first improvements, then more were made by Hall. The GE team used tungsten carbide anvils within a hydraulic press to squeeze the carbonaceous sample held in a catlinite container, the finished grit being squeezed out of the container into a gasket. The team recorded diamond synthesis on one occasion, but the experiment could not be reproduced because of uncertain synthesis conditions, and the diamond was later shown to have been a natural diamond used as a seed.

Hall achieved the first commercially successful synthesis of diamond on December 16, 1954, and this was announced on February 15, 1955. His breakthrough was using a "belt" press, which was capable of producing pressures above 10 GPa (1,500,000 psi) and temperatures above 2,000 °C (3,630 °F). The press used a pyrophyllite container in which graphite was dissolved within molten nickel, cobalt or iron. Those metals acted as a "solvent-catalyst", which both dissolved carbon and accelerated its conversion into diamond. The largest diamond he produced was 0.15 mm (0.0059 in) across; it was too small and visually imperfect for jewelry, but usable in industrial abrasives. Hall's co-workers were able to replicate his work, and the discovery was published in the major journal Nature. He was the first person to grow a synthetic diamond with a reproducible, verifiable and well-documented process. He left GE in 1955, and three years later developed a new apparatus for the synthesis of diamond—a tetrahedral press with four anvils—to avoid violating a U.S. Department of Commerce secrecy order on the GE patent applications.

Further development

A scalpel with single-crystal synthetic diamond blade

Synthetic gem-quality diamond crystals were first produced in 1970 by GE, then reported in 1971. The first successes used a pyrophyllite tube seeded at each end with thin pieces of diamond. The graphite feed material was placed in the center and the metal solvent (nickel) between the graphite and the seeds. The container was heated and the pressure was raised to about 5.5 GPa (800,000 psi). The crystals grow as they flow from the center to the ends of the tube, and extending the length of the process produces larger crystals. Initially, a week-long growth process produced gem-quality stones of around 5 mm (0.20 in) (1 carat or 0.2 g), and the process conditions had to be as stable as possible. The graphite feed was soon replaced by diamond grit because that allowed much better control of the shape of the final crystal.

The first gem-quality stones were always yellow to brown in color because of contamination with nitrogen. Inclusions were common, especially "plate-like" ones from the nickel. Removing all nitrogen from the process by adding aluminum or titanium produced colorless "white" stones, and removing the nitrogen and adding boron produced blue ones. Removing nitrogen also slowed the growth process and reduced the crystalline quality, so the process was normally run with nitrogen present.

Although the GE stones and natural diamonds were chemically identical, their physical properties were not the same. The colorless stones produced strong fluorescence and phosphorescence under short-wavelength ultraviolet light, but were inert under long-wave UV. Among natural diamonds, only the rarer blue gems exhibit these properties. Unlike natural diamonds, all the GE stones showed strong yellow fluorescence under X-rays. The De Beers Diamond Research Laboratory has grown stones of up to 25 carats (5.0 g) for research purposes. Stable HPHT conditions were kept for six weeks to grow high-quality diamonds of this size. For economic reasons, the growth of most synthetic diamonds is terminated when they reach a mass of 1 carat (200 mg) to 1.5 carats (300 mg).

In the 1950s, research started in the Soviet Union and the US on the growth of diamond by pyrolysis of hydrocarbon gases at the relatively low temperature of 800 °C (1,470 °F). This low-pressure process is known as chemical vapor deposition (CVD). William G. Eversole reportedly achieved vapor deposition of diamond over diamond substrate in 1953, but it was not reported until 1962. Diamond film deposition was independently reproduced by Angus and coworkers in 1968 and by Deryagin and Fedoseev in 1970. Whereas Eversole and Angus used large, expensive, single-crystal diamonds as substrates, Deryagin and Fedoseev succeeded in making diamond films on non-diamond materials (silicon and metals), which led to massive research on inexpensive diamond coatings in the 1980s.

From 2013, reports emerged of a rise in undisclosed synthetic melee diamonds (small round diamonds typically used to frame a central diamond or embellish a band) being found in set jewelry and within diamond parcels sold in the trade. Due to the relatively low cost of diamond melee, as well as relative lack of universal knowledge for identifying large quantities of melee efficiently, not all dealers have made an effort to test diamond melee to correctly identify whether it is of natural or man-made origin. However, international laboratories are now beginning to tackle the issue head-on, with significant improvements in synthetic melee identification being made.

Manufacturing technologies

There are several methods used to produce synthetic diamonds. The original method uses high pressure and high temperature (HPHT) and is still widely used because of its relatively low cost. The process involves large presses that can weigh hundreds of tons to produce a pressure of 5 GPa (730,000 psi) at 1,500 °C (2,730 °F). The second method, using chemical vapor deposition (CVD), creates a carbon plasma over a substrate onto which the carbon atoms deposit to form diamond. Other methods include explosive formation (forming detonation nanodiamonds) and sonication of graphite solutions.

High pressure, high temperature

Schematic of a belt press

In the HPHT method, there are three main press designs used to supply the pressure and temperature necessary to produce synthetic diamond: the belt press, the cubic press and the split-sphere (BARS) press. Diamond seeds are placed at the bottom of the press. The internal part of the press is heated above 1,400 °C (2,550 °F) and melts the solvent metal. The molten metal dissolves the high purity carbon source, which is then transported to the small diamond seeds and precipitates, forming a large synthetic diamond.

The original GE invention by Tracy Hall uses the belt press wherein the upper and lower anvils supply the pressure load to a cylindrical inner cell. This internal pressure is confined radially by a belt of pre-stressed steel bands. The anvils also serve as electrodes providing electric current to the compressed cell. A variation of the belt press uses hydraulic pressure, rather than steel belts, to confine the internal pressure. Belt presses are still used today, but they are built on a much larger scale than those of the original design.

The second type of press design is the cubic press. A cubic press has six anvils which provide pressure simultaneously onto all faces of a cube-shaped volume. The first multi-anvil press design was a tetrahedral press, using four anvils to converge upon a tetrahedron-shaped volume. The cubic press was created shortly thereafter to increase the volume to which pressure could be applied. A cubic press is typically smaller than a belt press and can more rapidly achieve the pressure and temperature necessary to create synthetic diamond. However, cubic presses cannot be easily scaled up to larger volumes: the pressurized volume can be increased by using larger anvils, but this also increases the amount of force needed on the anvils to achieve the same pressure. An alternative is to decrease the surface area to volume ratio of the pressurized volume, by using more anvils to converge upon a higher-order platonic solid, such as a dodecahedron. However, such a press would be complex and difficult to manufacture.

Schematic of a BARS system

The BARS apparatus is claimed to be the most compact, efficient, and economical of all the diamond-producing presses. In the center of a BARS device, there is a ceramic cylindrical "synthesis capsule" of about 2 cm³ (0.12 cu in) in size. The cell is placed into a cube of pressure-transmitting material, such as pyrophyllite ceramics, which is pressed by inner anvils made from cemented carbide (e.g., tungsten carbide or VK10 hard alloy). The outer octahedral cavity is pressed by 8 steel outer anvils. After mounting, the whole assembly is locked in a disc-type barrel with a diameter about 1 m (3 ft 3 in). The barrel is filled with oil, which pressurizes upon heating, and the oil pressure is transferred to the central cell. The synthesis capsule is heated up by a coaxial graphite heater, and the temperature is measured with a thermocouple.

Chemical vapor deposition

Further information: Chemical vapor deposition

 

Free-standing single-crystal CVD diamond disc

Chemical vapor deposition is a method by which diamond can be grown from a hydrocarbon gas mixture. Since the early 1980s, this method has been the subject of intensive worldwide research. Whereas the mass production of high-quality diamond crystals make the HPHT process the more suitable choice for industrial applications, the flexibility and simplicity of CVD setups explain the popularity of CVD growth in laboratory research. The advantages of CVD diamond growth include the ability to grow diamond over large areas and on various substrates, and the fine control over the chemical impurities and thus properties of the diamond produced. Unlike HPHT, CVD process does not require high pressures, as the growth typically occurs at pressures under 27 kPa (3.9 psi).

The CVD growth involves substrate preparation, feeding varying amounts of gases into a chamber and energizing them. The substrate preparation includes choosing an appropriate material and its crystallographic orientation; cleaning it, often with a diamond powder to abrade a non-diamond substrate; and optimizing the substrate temperature (about 800 °C (1,470 °F)) during the growth through a series of test runs. The gases always include a carbon source, typically methane, and hydrogen with a typical ratio of 1:99. Hydrogen is essential because it selectively etches off non-diamond carbon. The gases are ionized into chemically active radicals in the growth chamber using microwave power, a hot filament, an arc discharge, a welding torch, a laser, an electron beam, or other means.

During the growth, the chamber materials are etched off by the plasma and can incorporate into the growing diamond. In particular, CVD diamond is often contaminated by silicon originating from the silica windows of the growth chamber or from the silicon substrate. Therefore, silica windows are either avoided or moved away from the substrate. Boron-containing species in the chamber, even at very low trace levels, also make it unsuitable for the growth of pure diamond.

Detonation of explosives

Main article: Detonation nanodiamond

 

Electron micrograph (TEM) of detonation nanodiamond

Diamond nanocrystals (5 nm (2.0×10⁻⁷ in) in diameter) can be formed by detonating certain carbon-containing explosives in a metal chamber. These are called "detonation nanodiamonds". During the explosion, the pressure and temperature in the chamber become high enough to convert the carbon of the explosives into diamond. Being immersed in water, the chamber cools rapidly after the explosion, suppressing conversion of newly produced diamond into more stable graphite. In a variation of this technique, a metal tube filled with graphite powder is placed in the detonation chamber. The explosion heats and compresses the graphite to an extent sufficient for its conversion into diamond. The product is always rich in graphite and other non-diamond carbon forms, and requires prolonged boiling in hot nitric acid (about 1 day at 250 °C (482 °F)) to dissolve them. The recovered nanodiamond powder is used primarily in polishing applications. It is mainly produced in China, Russia and Belarus, and started reaching the market in bulk quantities by the early 2000s.

Ultrasound cavitation

Micron-sized diamond crystals can be synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation. The diamond yield is about 10% of the initial graphite weight. The estimated cost of diamond produced by this method is comparable to that of the HPHT method; the crystalline perfection of the product is significantly worse for the ultrasonic synthesis. This technique requires relatively simple equipment and procedures, but it has only been reported by two research groups, and has no industrial use. Numerous process parameters, such as preparation of the initial graphite powder, the choice of ultrasonic power, synthesis time and the solvent, are not yet optimized, leaving a window for potential improvement of the efficiency and reduction of the cost of the ultrasonic synthesis.

Properties

Traditionally, the absence of crystal flaws is considered to be the most important quality of a diamond. Purity and high crystalline perfection make diamonds transparent and clear, whereas its hardness, optical dispersion (luster), and chemical stability (combined with marketing), make it a popular gemstone. High thermal conductivity is also important for technical applications. Whereas high optical dispersion is an intrinsic property of all diamonds, their other properties vary depending on how the diamond was created.

Crystallinity

Diamond can be one single, continuous crystal or it can be made up of many smaller crystals (polycrystal). Large, clear and transparent single-crystal diamonds are typically used as gemstones. Polycrystalline diamond (PCD) consists of numerous small grains, which are easily seen by the naked eye through strong light absorption and scattering; it is unsuitable for gems and is used for industrial applications such as mining and cutting tools. Polycrystalline diamond is often described by the average size (or grain size) of the crystals that make it up. Grain sizes range from nanometers to hundreds of micrometers, usually referred to as "nanocrystalline" and "microcrystalline" diamond, respectively.

Hardness

The hardness of diamond is 10 on the Mohs scale of mineral hardness, the hardest known material on this scale. Diamond is also the hardest known material for its resistance to indentation. The hardness of synthetic diamond depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the direction (along the longest diagonal of the cubic diamond lattice). Nanocrystalline diamond produced through CVD diamond growth can have a hardness ranging from 30% to 75% of that of single crystal diamond, and the hardness can be controlled for specific applications. Some synthetic single-crystal diamonds and HPHT nanocrystalline diamonds (see hyperdiamond) are harder than any known natural diamond.

Impurities and inclusions

Main article: Crystallographic defects in diamond

Every diamond contains atoms other than carbon in concentrations detectable by analytical techniques. Those atoms can aggregate into macroscopic phases called inclusions. Impurities are generally avoided, but can be introduced intentionally as a way to control certain properties of the diamond. Growth processes of synthetic diamond, using solvent-catalysts, generally lead to formation of a number of impurity-related complex centers, involving transition metal atoms (such as nickel, cobalt or iron), which affect the electronic properties of the material.

For instance, pure diamond is an electrical insulator, but diamond with boron added is an electrical conductor (and, in some cases, a superconductor), allowing it to be used in electronic applications. Nitrogen impurities hinder movement of lattice dislocations (defects within the crystal structure) and put the lattice under compressive stress, thereby increasing hardness and toughness.

Thermal conductivity

The thermal conductivity of CVD diamond ranges from tens of W/m-K to more than 2000 W/m-K, depending on the defects, grain boundary structures. As the growth of diamond in CVD, the grains grow with the film thickness, leading to a gradient thermal conductivity along the film thickness direction.

Unlike most electrical insulators, pure diamond is an excellent conductor of heat because of the strong covalent bonding within the crystal. The thermal conductivity of pure diamond is the highest of any known solid. Single crystals of synthetic diamond enriched in ¹²
C
(99.9%), isotopically pure diamond, have the highest thermal conductivity of any material, 30 W/cm·K at room temperature, 7.5 times higher than that of copper. Natural diamond's conductivity is reduced by 1.1% by the ¹³
C
naturally present, which acts as an inhomogeneity in the lattice.

Diamond's thermal conductivity is made use of by jewelers and gemologists who may employ an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds.

Applications

Machining and cutting tools

Diamonds in an angle grinder blade

Most industrial applications of synthetic diamond have long been associated with their hardness; this property makes diamond the ideal material for machine tools and cutting tools. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial applications of this ability include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. These are by far the largest industrial applications of synthetic diamond. While natural diamond is also used for these purposes, synthetic HPHT diamond is more popular, mostly because of better reproducibility of its mechanical properties. Diamond is not suitable for machining ferrous alloys at high speeds, as carbon is soluble in iron at the high temperatures created by high-speed machining, leading to greatly increased wear on diamond tools compared to alternatives.

The usual form of diamond in cutting tools is micron-sized grains dispersed in a metal matrix (usually cobalt) sintered onto the tool. This is typically referred to in industry as polycrystalline diamond (PCD). PCD-tipped tools can be found in mining and cutting applications. For the past fifteen years, work has been done to coat metallic tools with CVD diamond, and though the work shows promise, it has not significantly replaced traditional PCD tools.

Thermal conductor

Most materials with high thermal conductivity are also electrically conductive, such as metals. In contrast, pure synthetic diamond has high thermal conductivity, but negligible electrical conductivity. This combination is invaluable for electronics where diamond is used as a heat sink for high-power laser diodes, laser arrays and high-power transistors. Efficient heat dissipation prolongs the lifetime of those electronic devices, and the devices' high replacement costs justify the use of efficient, though relatively expensive, diamond heat sinks. In semiconductor technology, synthetic diamond heat spreaders prevent silicon and other semiconducting devices from overheating.

Optical material

Diamond is hard, chemically inert, and has high thermal conductivity and a low coefficient of thermal expansion. These properties make diamond superior to any other existing window material used for transmitting infrared and microwave radiation. Therefore, synthetic diamond is starting to replace zinc selenide as the output window of high-power CO₂ lasers and gyrotrons. Those synthetic polycrystalline diamond windows are shaped as disks of large diameters (about 10 cm for gyrotrons) and small thicknesses (to reduce absorption) and can only be produced with the CVD technique. Single crystal slabs of dimensions of length up to approximately 10 mm are becoming increasingly important in several areas of optics including heatspreaders inside laser cavities, diffractive optics and as the optical gain medium in Raman lasers. Recent advances in the HPHT and CVD synthesis techniques have improved the purity and crystallographic structure perfection of single-crystalline diamond enough to replace silicon as a diffraction grating and window material in high-power radiation sources, such as synchrotrons. Both the CVD and HPHT processes are also used to create designer optically transparent diamond anvils as a tool for measuring electric and magnetic properties of materials at ultra high pressures using a diamond anvil cell.

Electronics

Synthetic diamond has potential uses as a semiconductor, because it can be doped with impurities like boron and phosphorus. Since these elements contain one more or one fewer valence electron than carbon, they turn synthetic diamond into p-type or n-type semiconductor. Making a p–n junction by sequential doping of synthetic diamond with boron and phosphorus produces light-emitting diodes (LEDs) producing UV light of 235 nm. Another useful property of synthetic diamond for electronics is high carrier mobility, which reaches 4500 cm²/(V·s) for electrons in single-crystal CVD diamond. High mobility is favorable for high-frequency operation and field-effect transistors made from diamond have already demonstrated promising high-frequency performance above 50 GHz. The wide band gap of diamond (5.5 eV) gives it excellent dielectric properties. Combined with the high mechanical stability of diamond, those properties are being used in prototype high-power switches for power stations.

Synthetic diamond transistors have been produced in the laboratory. They remain functional at much higher temperatures than silicon devices, and are resistant to chemical and radiation damage. While no diamond transistors have yet been successfully integrated into commercial electronics, they are promising for use in exceptionally high-power situations and hostile non-oxidizing environments.

Synthetic diamond is already used as radiation detection device. It is radiation hard and has a wide bandgap of 5.5 eV (at room temperature). Diamond is also distinguished from most other semiconductors by the lack of a stable native oxide. This makes it difficult to fabricate surface MOS devices, but it does create the potential for UV radiation to gain access to the active semiconductor without absorption in a surface layer. Because of these properties, it is employed in applications such as the BaBar detector at the Stanford Linear Accelerator and BOLD (Blind to the Optical Light Detectors for VUV solar observations). A diamond VUV detector recently was used in the European LYRA program.

Conductive CVD diamond is a useful electrode under many circumstances. Photochemical methods have been developed for covalently linking DNA to the surface of polycrystalline diamond films produced through CVD. Such DNA-modified films can be used for detecting various biomolecules, which would interact with DNA thereby changing electrical conductivity of the diamond film. In addition, diamonds can be used to detect redox reactions that cannot ordinarily be studied and in some cases degrade redox-reactive organic contaminants in water supplies. Because diamond is mechanically and chemically stable, it can be used as an electrode under conditions that would destroy traditional materials. As an electrode, synthetic diamond can be used in waste water treatment of organic effluents and the production of strong oxidants.

Gemstones

Main article: Diamond (gemstone)

 

Colorless gem cut from diamond grown by chemical vapor deposition

Synthetic diamonds for use as gemstones are grown by HPHT or CVD methods, and represented approximately 2% of the gem-quality diamond market as of 2013. However, there are indications that the market share of synthetic jewelry-quality diamonds may grow as advances in technology allow for larger higher-quality synthetic production on a more economic scale. They are available in yellow, pink, green, orange, blue and, to a lesser extent, colorless (or white). The yellow color comes from nitrogen impurities in the manufacturing process, while the blue color comes from boron. Other colors, such as pink or green, are achievable after synthesis using irradiation. Several companies also offer memorial diamonds grown using cremated remains.

Gem-quality diamonds grown in a lab can be chemically, physically and optically identical to naturally occurring ones. The mined diamond industry has undertaken legal, marketing and distribution countermeasures to try to protect its market from the emerging presence of synthetic diamonds. Synthetic diamonds can be distinguished by spectroscopy in the infrared, ultraviolet, or X-ray wavelengths. The DiamondView tester from De Beers uses UV fluorescence to detect trace impurities of nitrogen, nickel or other metals in HPHT or CVD diamonds.

At least one maker of laboratory-grown diamonds has made public statements about being "committed to disclosure" of the nature of its diamonds, and laser-inscribed serial numbers on all of its gemstones. The company web site shows an example of the lettering of one of its laser inscriptions, which includes both the words "Gemesis created" and the serial number prefix "LG" (laboratory grown).

In May 2015, a record was set for an HPHT colorless diamond at 10.02 carats. The faceted jewel was cut from a 32.2-carat stone that was grown in about 300 hours. By 2022, gem-quality diamonds of 16–20 carats were being produced.

Traditional diamond mining has led to human rights abuses in Africa and other diamond mining countries. The 2006 Hollywood movie Blood Diamond helped to publicize the problem. Consumer demand for synthetic diamonds has been increasing, albeit from a small base, as customers look for stones that are ethically sound and cheaper. Any kind of mining also causes irreversible changes to the bio-diversity.

According to a report from the Gem & Jewellery Export Promotional Council, synthetic diamonds accounted for 0.28% of diamond produced for use as gemstones in 2014. In April 2022, CNN Business reported that engagement rings featuring a synthetic or a lab grown diamond jumped 63% compared to previous year, while the number of engagement rings sold with a natural diamond declined 25% in the same period.

Around 2016, the price of synthetic diamond gemstones (e.g., 1 carat stones) began dropping "precipitously" by roughly 30% in one year, becoming clearly lower than that of mined diamonds. As of 2017, synthetic diamonds sold as jewelry were typically selling for 15–20% less than natural equivalents; the relative price was expected to decline further as production economics improve.

In May 2018, De Beers announced that it would introduce a new jewelry brand called "Lightbox" that features synthetic diamonds.

In July 2018, the U.S. Federal Trade Commission approved a substantial revision to its Jewelry Guides, with changes that impose new rules on how the trade can describe diamonds and diamond simulants. The revised guides were substantially contrary to what had been advocated in 2016 by De Beers. The new guidelines remove the word "natural" from the definition of "diamond", thus including lab-grown diamonds within the scope of the definition of "diamond". The revised guide further states that "If a marketer uses 'synthetic' to imply that a competitor's lab-grown diamond is not an actual diamond, ... this would be deceptive." In July 2019, the third party diamond certification lab GIA (Gemological Institute of America) dropped of the word 'synthetic' in its certification process and report for lab-grown diamonds, according to the FTC revision.