Energy levels for an electron in an atom: ground state and excited states. After absorbing energy, an electron may "jump" from the ground state to a higher energy excited state.
A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy, called energy levels. This contrasts with classical particles, which can have any amount of energy. The term is commonly used for the energy levels of the electrons in atoms, ions, or molecules, which are bound by the electric field of the nucleus, but can also refer to energy levels of nuclei or vibrational or rotational energy levels in molecules. The energy spectrum of a system with such discrete energy levels is said to be quantized.
In chemistry and atomic physics, an electron shell, or principal energy level, may be thought of as the orbit of one or more electrons around an atom's nucleus.
The closest shell to the nucleus is called the "1 shell" (also called
"K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell"
(or "M shell"), and so on farther and farther from the nucleus. The
shells correspond with the principal quantum numbers (n = 1, 2, 3, 4, ...) or are labeled alphabetically with letters used in the X-ray notation (K, L, M, N, ...).
Each shell can contain only a fixed number of electrons: The
first shell can hold up to two electrons, the second shell can hold up
to eight (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 +
10) and so on. The general formula is that the nth shell can in principle hold up to 2n2 electrons. Since electrons are electrically attracted
to the nucleus, an atom's electrons will generally occupy outer shells
only if the more inner shells have already been completely filled by
other electrons. However, this is not a strict requirement: atoms may
have two or even three incomplete outer shells. (See Madelung rule for more details.) For an explanation of why electrons exist in these shells see electron configuration.
If an atom, ion, or molecule is at the lowest possible energy level, it and its electrons are said to be in the ground state. If it is at a higher energy level, it is said to be excited, or any electrons that have higher energy than the ground state are excited. An energy level is regarded as degenerate if there is more than one measurable quantum mechanical state associated with it.
Explanation
Wavefunctions of a hydrogen
atom, showing the probability of finding the electron in the space
around the nucleus. Each stationary state defines a specific energy
level of the atom.
Quantized energy levels result from the wave behavior of particles,
which gives a relationship between a particle's energy and its wavelength. For a confined particle such as an electron in an atom, the wave functions that have well defined energies have the form of a standing wave. States having well-defined energies are called stationary states
because they are the states that do not change in time. Informally,
these states correspond to a whole number of wavelengths of the wavefunction
along a closed path (a path that ends where it started), such as a
circular orbit around an atom, where the number of wavelengths gives the
type of atomic orbital
(0 for s-orbitals, 1 for p-orbitals and so on). Elementary examples
that show mathematically how energy levels come about are the particle in a box and the quantum harmonic oscillator.
Any superposition (linear combination)
of energy states is also a quantum state, but such states change with
time and do not have well-defined energies. A measurement of the energy
results in the collapse
of the wavefunction, which results in a new state that consists of just
a single energy state. Measurement of the possible energy levels of an
object is called spectroscopy.
In
the formulas for energy of electrons at various levels given below in
an atom, the zero point for energy is set when the electron in question
has completely left the atom; i.e. when the electron's principal quantum numbern = ∞. When the electron is bound to the atom in any closer value of n, the electron's energy is lower and is considered negative.
Orbital state energy level: atom/ion with nucleus + one electron
Assume there is one electron in a given atomic orbital in a hydrogen-like atom (ion).
The energy of its state is mainly determined by the electrostatic
interaction of the (negative) electron with the (positive) nucleus. The
energy levels of an electron around a nucleus are given by:
An equivalent formula can be derived quantum mechanically from the time-independent Schrödinger equation with a kinetic energy Hamiltonian operator using a wave function as an eigenfunction to obtain the energy levels as eigenvalues, but the Rydberg constant would be replaced by other fundamental physics constants.
Electron–electron interactions in atoms
If
there is more than one electron around the atom, electron–electron
interactions raise the energy level. These interactions are often
neglected if the spatial overlap of the electron wavefunctions is low.
For multi-electron atoms, interactions between electrons cause
the preceding equation to be no longer accurate as stated simply with Z as the atomic number. A simple (though not complete) way to understand this is as a shielding effect,
where the outer electrons see an effective nucleus of reduced charge,
since the inner electrons are bound tightly to the nucleus and partially
cancel its charge. This leads to an approximate correction where Z is substituted with an effective nuclear charge symbolized as Zeff that depends strongly on the principal quantum number.
In such cases, the orbital types (determined by the azimuthal quantum numberℓ) as well as their levels within the molecule affect Zeff and therefore also affect the various atomic electron energy levels. The Aufbau principle of filling an atom with electrons for an electron configuration takes these differing energy levels into account. For filling an atom with electrons in the ground state, the lowest energy levels are filled first and consistent with the Pauli exclusion principle, the Aufbau principle, and Hund's rule.
Fine structure splitting
Fine structure arises from relativistic kinetic energy corrections, spin–orbit coupling (an electrodynamic interaction between the electron's spin and motion and the nucleus's electric field) and the Darwin term (contact term interaction of s shell electrons inside the nucleus). These affect the levels by a typical order of magnitude of 10−3 eV.
This even finer structure is due to electron–nucleus spin–spin interaction, resulting in a typical change in the energy levels by a typical order of magnitude of 10−4 eV.
Chemical bonds
between atoms in a molecule form because they make the situation more
stable for the involved atoms, which generally means the sum energy
level for the involved atoms in the molecule is lower than if the atoms
were not so bonded. As separate atoms approach each other to covalently bond, their orbitals affect each other's energy levels to form bonding and antibonding molecular orbitals. The energy level of the bonding orbitals is lower, and the energy level of the antibonding orbitals
is higher. For the bond in the molecule to be stable, the covalent
bonding electrons occupy the lower energy bonding orbital, which may be
signified by such symbols as σ or π depending on the situation.
Corresponding anti-bonding orbitals can be signified by adding an
asterisk to get σ* or π* orbitals. A non-bonding orbital in a molecule is an orbital with electrons in outer shells
which do not participate in bonding and its energy level is the same as
that of the constituent atom. Such orbitals can be designated as n orbitals. The electrons in an n orbital are typically lone pairs. In polyatomic molecules, different vibrational and rotational energy levels are also involved.
The molecular energy levels are labelled by the molecular term symbols. The specific energies of these components vary with the specific energy state and the substance.
Energy level diagrams
There are various types of energy level diagrams for bonds between atoms in a molecule.
An increase in energy level from E1 to E2 resulting from absorption of a photon represented by the red squiggly arrow, and whose energy is hν.A decrease in energy level from E2 to E1 resulting in emission of a photon represented by the red squiggly arrow, and whose energy is hν.
Electrons in atoms and molecules can change (make transitions in) energy levels by emitting or absorbing a photon (of electromagnetic radiation), whose energy must be exactly equal to the energy difference between the two levels.
Electrons can also be completely removed from a chemical species such as an atom, molecule, or ion. Complete removal of an electron from an atom can be a form of ionization, which is effectively moving the electron out to an orbital with an infinite principal quantum number,
in effect so far away so as to have practically no more effect on the
remaining atom (ion). For various types of atoms, there are 1st, 2nd,
3rd, etc. ionization energies
for removing the 1st, then the 2nd, then the 3rd, etc. of the highest
energy electrons, respectively, from the atom originally in the ground state. Energy in corresponding opposite quantities can also be released, sometimes in the form of photon energy, when electrons are added to positively charged ions or sometimes atoms. Molecules can also undergo transitions in their vibrational
or rotational energy levels. Energy level transitions can also be
nonradiative, meaning emission or absorption of a photon is not
involved.
If an atom, ion, or molecule is at the lowest possible energy level, it and its electrons are said to be in the ground state. If it is at a higher energy level, it is said to be excited, or any electrons that have higher energy than the ground state are excited. Such a species can be excited to a higher energy level by absorbing
a photon whose energy is equal to the energy difference between the
levels. Conversely, an excited species can go to a lower energy level by
spontaneously emitting a photon equal to the energy difference. A
photon's energy is equal to the Planck constant (h) times its frequency (f) and thus is proportional to its frequency, or inversely to its wavelength (λ).
ΔE = hf = hc / λ,
since c, the speed of light, equals to fλ
Correspondingly, many kinds of spectroscopy are based on detecting the frequency or wavelength of the emitted or absorbed
photons to provide information on the material analyzed, including
information on the energy levels and electronic structure of materials
obtained by analyzing the spectrum.
An asterisk is commonly used to designate an excited state. An
electron transition in a molecule's bond from a ground state to an
excited state may have a designation such as σ → σ*, π → π*, or n → π*
meaning excitation of an electron from a σ bonding to a σ antibonding orbital, from a π bonding to a π antibonding orbital, or from an n non-bonding to a π antibonding orbital.
Reverse electron transitions for all these types of excited molecules
are also possible to return to their ground states, which can be
designated as σ* → σ, π* → π, or π* → n.
A transition in an energy level of an electron in a molecule may be combined with a vibrational transition and called a vibronic transition. A vibrational and rotational transition may be combined by rovibrational coupling. In rovibronic coupling,
electron transitions are simultaneously combined with both vibrational
and rotational transitions. Photons involved in transitions may have
energy of various ranges in the electromagnetic spectrum, such as X-ray, ultraviolet, visible light, infrared, or microwave
radiation, depending on the type of transition. In a very general way,
energy level differences between electronic states are larger,
differences between vibrational levels are intermediate, and differences
between rotational levels are smaller, although there can be overlap. Translational energy levels are practically continuous and can be calculated as kinetic energy using classical mechanics.
Higher temperature
causes fluid atoms and molecules to move faster increasing their
translational energy, and thermally excites molecules to higher average
amplitudes of vibrational and rotational modes (excites the molecules to
higher internal energy levels). This means that as temperature rises,
translational, vibrational, and rotational contributions to molecular heat capacity let molecules absorb heat and hold more internal energy. Conduction of heat typically occurs as molecules or atoms collide transferring the heat
between each other. At even higher temperatures, electrons can be
thermally excited to higher energy orbitals in atoms or molecules. A
subsequent drop of an electron to a lower energy level can release a
photon, causing a possibly coloured glow.
An electron farther from the nucleus has higher potential energy
than an electron closer to the nucleus, thus it becomes less bound to
the nucleus, since its potential energy is negative and inversely
dependent on its distance from the nucleus.
Crystalline materials
Crystalline solids are found to have energy bands,
instead of or in addition to energy levels. Electrons can take on any
energy within an unfilled band. At first this appears to be an exception
to the requirement for energy levels. However, as shown in band theory,
energy bands are actually made up of many discrete energy levels which
are too close together to resolve. Within a band the number of levels is
of the order of the number of atoms in the crystal, so although
electrons are actually restricted to these energies, they appear to be
able to take on a continuum of values. The important energy levels in a
crystal are the top of the valence band, the bottom of the conduction band, the Fermi level, the vacuum level, and the energy levels of any defect states in the crystal.
After absorbing energy, an electron may jump from the ground state to a higher energy excited state.Excitations of copper 3d orbitals on the CuO2 plane of a high-Tc superconductor. The ground state (blue) is x2–y2 orbitals; the excited orbitals are in green; the arrows illustrate inelastic x-ray spectroscopy.
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to an increase in energy level above a chosen starting point, usually the ground state, but sometimes an already excited state. The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that exhibit negative temperature).
The lifetime of a system in an excited state is usually short: spontaneous or induced emission of a quantum of energy (such as a photon or a phonon)
usually occurs shortly after the system is promoted to the excited
state, returning the system to a state with lower energy (a less excited
state or the ground state). This return to a lower energy level is
often loosely described as decay and is the inverse of excitation.
Atoms can be excited by heat, electricity, or light. The hydrogen atom provides a simple example of this concept.
The ground state of the hydrogen atom has the atom's single electron in the lowest possible orbital (that is, the spherically symmetric "1s" wave function, which, so far, has been demonstrated to have the lowest possible quantum numbers). By giving the atom additional energy (for example, by absorption of a photon
of an appropriate energy), the electron moves into an excited state
(one with one or more quantum numbers greater than the minimum
possible). When the electron finds itself between two states, a shift
which happens very fast, it's in a superposition of both states. If the photon has too much energy, the electron will cease to be bound to the atom, and the atom will become ionized.
After excitation the atom may return to the ground state or a
lower excited state, by emitting a photon with a characteristic energy.
Emission of photons from atoms in various excited states leads to an electromagnetic spectrum showing a series of characteristic emission lines (including, in the case of the hydrogen atom, the Lyman, Balmer, Paschen and Brackett series).
An atom in a high excited state is termed a Rydberg atom. A system of highly excited atoms can form a long-lived condensed excited state, Rydberg matter.
Perturbed gas excitation
A
collection of molecules forming a gas can be considered in an excited
state if one or more molecules are elevated to kinetic energy levels
such that the resulting velocity distribution departs from the
equilibrium Boltzmann distribution. This phenomenon has been studied in the case of a two-dimensional gas in some detail, analyzing the time taken to relax to equilibrium.
The
excitation of a system (an atom or molecule) from one excited state to a
higher-energy excited state with the absorption of a photon is called excited-state absorption
(ESA). Excited-state absorption is possible only when an electron has
been already excited from the ground state to a lower excited state. The
excited-state absorption is usually an undesired effect, but it can be
useful in upconversion pumping. Excited-state absorption measurements are done using pump–probe techniques such as flash photolysis.
However, it is not easy to measure them compared to ground-state
absorption, and in some cases complete bleaching of the ground state is
required to measure excited-state absorption.
Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster.
A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineralcrystal which, when cut or polished, is used to make jewelry or other adornments. Certain rocks (such as lapis lazuli, opal, and obsidian) and occasionally organic materials that are not minerals (such as amber, jet, and pearl) may also be used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some softer minerals such as brazilianite may be used in jewelry because of their color or luster or other physical properties that have aesthetic value.
However, generally speaking, soft minerals are not typically used as
gemstones by virtue of their brittleness and lack of durability.
Found all over the world, the industry of coloured gemstones
(i.e. anything other than diamonds) is currently estimated at around US$
1.55 billion as of 2023 and is projected to steadily increase to a
value of US$ 4.46 billion by 2033.
A collection of gemstone pebbles made by tumbling the rough stones, except the ruby and tourmaline, with abrasive grit inside a rotating barrel. The largest pebble here is 40 mm (1.6 in) long.
The traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. In modern use, the precious stones are emerald, ruby, sapphire and diamond, with all other gemstones being semi-precious. This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent,
with fine color in their purest forms (except for the colorless
diamond), and very hard with a hardness score of 8 to 10 on the Mohs scale. Other stones are classified by their color, translucency, and hardness. The traditional distinction does not necessarily reflect modern values; for example, while garnets are relatively inexpensive, a green garnet called tsavorite can be far more valuable than a mid-quality emerald. Another traditional term for semi-precious gemstones used in art history and archaeology is hardstone.
Use of the terms 'precious' and 'semi-precious' in a commercial context
is, arguably, misleading in that it suggests certain stones are more
valuable than others when this is not reflected in the actual market
value, although it would generally be correct if referring to
desirability.
In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al 2O 3). Many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example, diamonds, which have a cubic crystal system, are often found as octahedrons.
Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink), which are all varieties of the mineral species beryl.
Gems are characterized in terms of their color (hue, tone and saturation), optical phenomena, luster, refractive index, birefringence, dispersion, specific gravity, hardness, cleavage, and fracture.They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.
Gemstones may also be classified in terms of their "water". This is a
recognized grading of the gem's luster, transparency, or "brilliance". Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency. Additionally, material or flaws within a stone may be present as inclusions.
Value
Spanish emerald and gold pendant at Victoria and Albert MuseumEnamelled gold, amethyst, and pearl pendant, about 1880, Pasquale Novissimo (1844–1914), V&A Museum number M.36-1928
Gemstones have no universally accepted grading system. Diamonds are graded using a system developed by the Gemological Institute of America
(GIA) in the early 1950s. Historically, all gemstones were graded using
the naked eye. The GIA system included a major innovation: the
introduction of 10x magnification as the standard for grading clarity.
Other gemstones are still graded using the naked eye (assuming 20/20
vision).
A mnemonic device,
the "four Cs" (color, cut, clarity, and carats), has been introduced to
help describe the factors used to grade a diamond. With modification,
these categories can be useful in understanding the grading of all
gemstones. The four criteria carry different weights depending upon
whether they are applied to colored gemstones or to colorless diamonds.
In diamonds, the cut is the primary determinant of value, followed by
clarity and color. An ideally cut diamond will sparkle, to break down
light into its constituent rainbow colors (dispersion), chop it up into
bright little pieces (scintillation), and deliver it to the eye
(brilliance). In its rough crystalline form, a diamond will do none of
these things; it requires proper fashioning and this is called "cut". In
gemstones that have color, including colored diamonds, the purity, and
beauty of that color is the primary determinant of quality.
Physical characteristics that make a colored stone valuable are
color, clarity to a lesser extent (emeralds will always have a number of
inclusions), cut, unusual optical phenomena within the stone such as color zoning (the uneven distribution of coloring within a gem) and asteria (star effects).
Apart from the more generic and commonly used gemstones such as from diamonds, rubies, sapphires, and emeralds, pearls and opal have also been defined as precious in the jewellery trade. Up to the discoveries of bulk amethyst
in Brazil in the 19th century, amethyst was considered a "precious
stone" as well, going back to ancient Greece. Even in the last century
certain stones such as aquamarine, peridot and cat's eye (cymophane)
have been popular and hence been regarded as precious, thus reinforcing
the notion that a mineral's rarity may have been implicated in its
classification as a precious stone and thus contribute to its value.
Today the gemstone trade no longer makes such a distinction.
Many gemstones are used in even the most expensive jewelry, depending
on the brand-name of the designer, fashion trends, market supply,
treatments, etc. Nevertheless, diamonds, rubies, sapphires, and emeralds
still have a reputation that exceeds those of other gemstones.
Rare or unusual gemstones, generally understood to include those
gemstones which occur so infrequently in gem quality that they are
scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite, painite and red beryl.
Gemstone pricing and value are governed by factors and
characteristics in the quality of the stone. These characteristics
include clarity, rarity, freedom from defects, the beauty of the stone,
as well as the demand for such stones. There are different pricing
influencers for both colored gemstones, and for diamonds. The pricing on
colored stones is determined by market supply-and-demand, but diamonds
are more intricate.
In the addition to the aesthetic and adorning/ornamental purpose of gemstones, there are many proponents of energy medicine who also value gemstones on the basis of their alleged healing powers.
A gemstone that has been rising in popularity is Cuprian Elbaite
Tourmaline which is also called "Paraiba Tourmaline". It was first
discovered in the late 1980s in Paraíba, Brazil and later in Mozambique
and Nigeria.
It is famous for its glowing neon blue color. Paraiba Tourmaline has
become one of the most popular gemstones in recent times thanks to its
color and is considered to be one of the important gemstones after
rubies, emeralds, and sapphires according to Gübelin Gemlab. Even though
it is a tourmaline, Paraiba Tourmaline is one of the most expensive
gemstones.
Grading
There are a number of laboratories which grade and provide reports on gemstones.
Hoge Raad Voor Diamant
(HRD Antwerp), The Diamond High Council, Belgium is one of Europe's
oldest laboratories; its main stakeholder is the Antwerp World Diamond
Centre
American Gem Trade Laboratory which is part of the American Gem
Trade Association (AGTA), a trade organization of jewelers and dealers
of colored stones
American Gemological Laboratories (AGL), owned by Christopher P. Smith
European Gemological Laboratory (EGL), founded in 1974 by Guy Margel in Belgium
Gemmological Association of All Japan (GAAJ-ZENHOKYO), Zenhokyo, Japan, active in gemological research
The Gem and Jewelry Institute of Thailand (Public Organization) or
GIT, Thailand's national institute for gemological research and gem
testing, Bangkok
Gemmology Institute of Southern Africa, Africa's premium gem laboratory
Swiss Gemmological Institute (SSEF), founded by Henry Hänni, focusing on colored gemstones and the identification of natural pearls
Gübelin Gem Lab, the traditional Swiss lab founded by Eduard Gübelin
Each laboratory has its own methodology to evaluate gemstones. A
stone can be called "pink" by one lab while another lab calls it
"padparadscha". One lab can conclude a stone is untreated, while another
lab might conclude that it is heat-treated.
To minimize such differences, seven of the most respected labs,
AGTA-GTL (New York), CISGEM (Milano), GAAJ-ZENHOKYO (Tokyo), GIA
(Carlsbad), GIT (Bangkok), Gübelin (Lucerne) and SSEF (Basel), have
established the Laboratory Manual Harmonisation Committee (LMHC), for
the standardization of wording reports, promotion of certain analytical
methods and interpretation of results. Country of origin has sometimes
been difficult to determine, due to the constant discovery of new source
locations. Determining a "country of origin" is thus much more
difficult than determining other aspects of a gem (such as cut, clarity,
etc.).
Gem dealers are aware of the differences between gem laboratories
and will make use of the discrepancies to obtain the best possible
certificate.
A few gemstones are used as gems in the crystal or other forms in
which they are found. Most, however, are cut and polished for usage as
jewelry. The two main classifications are as follows:
Stones cut as smooth, dome-shaped stones called cabochons or simply cab. These have been a popular shape since ancient time and is more durable than faceted gems.
Stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at exact angles.
Stones which are opaque or semi-opaque such as opal, turquoise, variscite,
etc. are commonly cut as cabochons. These gems are designed to show the
stone's color, luster and other surface properties as opposed to
internal reflection properties like brilliance. Grinding wheels and polishing agents are used to grind, shape, and polish the smooth dome shape of the stones.
Gems that are transparent are normally faceted, a method that
shows the optical properties of the stone's interior to its best
advantage by maximizing reflected light which is perceived by the viewer
as sparkle. There are many commonly used shapes for faceted stones. The facets must be cut at the proper angles, which varies depending on the optical
properties of the gem. If the angles are too steep or too shallow, the
light will pass through and not be reflected back toward the viewer. The
faceting machine is used to hold the stone onto a flat lap for cutting
and polishing the flat facets. Rarely, some cutters use special curved laps to cut and polish curved facets.
Colors
Nearly 300 variations of diamond color exhibited at the Aurora display at the Natural History Museum in LondonA variety of semiprecious stones in a piece of jewellery
The color of any material is due to the nature of light itself.
Daylight, often called white light, is all of the colors of the spectrum
combined. When light strikes a material, most of the light is absorbed
while a smaller amount of a particular frequency or wavelength is
reflected. The part that is reflected reaches the eye as the perceived
color. A ruby appears red because it absorbs all other colors of white light while reflecting red.
A material which is mostly the same can exhibit different colors.
For example, ruby and sapphire have the same primary chemical
composition (both are corundum)
but exhibit different colors because of impurities which absorb and
reflect different wavelengths of light depending on their individual
compositions. Even the same named gemstone can occur in many different
colors: sapphires show different shades of blue and pink and "fancy
sapphires" exhibit a whole range of other colors from yellow to
orange-pink, the latter called "padparadscha sapphire".
This difference in color is based on the atomic structure of the
stone. Although the different stones formally have the same chemical
composition and structure, they are not exactly the same. Every now and
then an atom is replaced by a completely different atom, sometimes as
few as one in a million atoms. These so-called impurities are sufficient to absorb certain colors and leave the other colors unaffected. For example, beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If manganese is added instead of chromium, beryl becomes pink morganite. With iron, it becomes aquamarine.Some gemstone treatments make use of the fact that these impurities can be "manipulated", thus changing the color of the gem.
Treatment
Gemstones are often treated to enhance the color or clarity of the stone.
In some cases, the treatment applied to the gemstone can also increase
its durability. Even though natural gemstones can be transformed using
the traditional method of cutting and polishing, other treatment options
allow the stone's appearance to be enhanced.
Depending on the type and extent of treatment, they can affect the
value of the stone. Some treatments are used widely because the
resulting gem is stable, while others are not accepted most commonly
because the gem color is unstable and may revert to the original tone.
Early history
Before
the innovation of modern-day tools, thousands of years ago, people were
recorded to use a variety of techniques to treat and enhance gemstones.
Some of the earliest methods of gemstone treatment date back to the
Minoan Age, for example foiling, which is where metal foil is used to
enhance a gemstone's colour. Other methods recorded 2000 years ago in the book Natural History by Pliny the Elder include oiling and dyeing/staining.
Heat
Heat
can either improve or spoil gemstone color or clarity. The heating
process has been well known to gem miners and cutters for centuries, and
in many stone types heating is a common practice. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in "ametrine" – a stone partly amethyst and partly citrine. Aquamarine
is often heated to remove yellow tones, or to change green colors into
the more desirable blue, or enhance its existing blue color to a deeper
blue.
Nearly all tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue / purple color. A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity.
When jewelry containing diamonds is heated for repairs, the diamond should be protected with boric acid;
otherwise, the diamond, which is pure carbon, could be burned on the
surface or even burned completely up. When jewelry containing sapphires or rubies
is heated, those stones should not be coated with boric acid (which can
etch the surface) or any other substance. They do not have to be
protected from burning, like a diamond (although the stones do need to
be protected from heat stress fracture by immersing the part of the
jewelry with stones in the water when metal parts are heated).
The irradiation process is widely practiced in jewelry industry and enabled the creation of gemstone colors that do not exist or are extremely rare in nature. However, particularly when done in a nuclear reactor,
the processes can make gemstones radioactive. Health risks related to
the residual radioactivity of the treated gemstones have led to
government regulations in many countries.
Virtually all blue topaz,
both the lighter and the darker blue shades such as "London" blue, has
been irradiated to change the color from white to blue. Most green
quartz (Oro Verde) are also irradiated to achieve the yellow-green
color. Diamonds are mainly irradiated to become blue-green or green,
although other colors are possible. When light-to-medium-yellow diamonds
are treated with gamma rays they may become green; with a high-energy
electron beam, blue.
Waxing/oiling
Emeralds containing natural fissures are sometimes filled with wax or oil
to disguise them. This wax or oil is also colored to make the emerald
appear of better color as well as clarity. Turquoise is also commonly
treated in a similar manner.
Fracture filling
The foreign material inside this fracture-filled emerald appears rainbow-colored under darkfield illumination.
Fracture filling has been in use with different gemstones such as
diamonds, emeralds, and sapphires. In 2006 "glass-filled rubies"
received publicity. Rubies over 10 carats (2 g) with large fractures
were filled with lead glass, thus dramatically improving the appearance
(of larger rubies in particular). Such treatments are fairly easy to
detect.
Bleaching
Pearls are a gemstone that is commonly treated with hydrogen peroxide to remove unwanted colours
Another treatment method that is commonly used to treat gemstones is
bleaching. This method uses a chemical in order to reduce the colour of
the gem. After bleaching, a combination treatment can be done by dying
the gemstone once the unwanted colours are removed. Hydrogen peroxide is
the most commonly used product used to alter gemstones and have notably
been used to treat jade and pearls. The treatment of bleaching can also
be followed by impregnation, which allows the gemstone's durability to
be increased.
Socioeconomic issues in the gemstone industry
The
socio-economic dynamics of the gemstone industry are shaped by market
forces and consumer preferences and typically go undiscussed. Changes in
demand and prices can significantly affect the livelihoods of those
involved in gemstone mining and trade, particularly in developing countries where the industry serves as a crucial source of income.
A situation that arises as a result of this is the exploitation of natural resources
and labor within gemstone mining operations. Many mines, particularly
in developing countries, face challenges such as inadequate safety
measures, low wages, and poor working conditions. Miners, often from disadvantaged backgrounds, endure hazardous working conditions and receive meager wages, contributing to cycles of poverty and exploitation. Gemstone mining
operations are frequently conducted in remote or underdeveloped areas,
lacking proper infrastructure and access to essential services such as
healthcare and education. This further contributes to the pre-existing socio-economic disparities
and obstructs community development such that the benefits of gemstone
extraction may not adequately reach those directly involved in the
process.
Another such issue revolves around environmental degradation
resulting from mining activities. Environmental degradation can pose
long-term threats to ecosystems and biodiversity, further worsening the
socio-economic state in affected regions. Unregulated mining practices often result in deforestation, soil erosion, and water contamination thus threatening ecosystems and biodiversity. Unregulated mining activity can also cause depletion of natural resources, thus diminishing the prospects for sustainable development.
The environmental impact of gemstone mining not only poses a threat to
ecosystems but also undermines the long-term viability of the industry
by diminishing the quality and quantity of available resources.
Furthermore, the gemstone industry is also susceptible to issues
related to transparency and ethics, which impact both producers and
consumers. The lack of standardized certification processes and the
prevalence of illicit practices undermine market integrity and trust.
The lack of transparency and accountability in the supply chain
aggravates pre-existing inequalities, as middlemen and corporations
often capture a disproportionate share of the profits. As a result the
unequal distribution of profits along the supply chain does little to improve socio-economic inequalities, particularly in regions where gemstones are mined.
Addressing these socio-economic challenges requires intensive
effort from various stakeholders, including governments, industry
executives, and society, to promote sustainable practices and ensure
equitable outcomes for all involved parties. Implementing and enforcing
regulations to ensure fair labor practices, environmental
sustainability, and ethical sourcing is essential. Additionally,
investing in community development projects, such as education and
healthcare initiatives, can help alleviate poverty and empower
marginalized communities dependent on the gemstone industry.
Collaboration across sectors is crucial for fostering a more equitable
and sustainable gemstone trade that benefits both producers and
consumers while respecting human rights and environmental integrity.
Synthetic and artificial gemstones
Synthetic gemstones are distinct from imitation or simulated gems.
Synthetic gems are physically, optically, and chemically identical to the natural stone, but are created in a laboratory.
Imitation or simulated stones are chemically different from the natural
stone, but may appear quite similar to it; they can be more easily
manufactured synthetic gemstones of a different mineral (spinel), glass, plastic, resins, or other compounds.
Examples of simulated or imitation stones include cubic zirconia, composed of zirconium oxide, synthetic moissanite, and uncolored, synthetic corundum or spinels; all of which are diamond simulants.
The simulants imitate the look and color of the real stone but possess
neither their chemical nor physical characteristics. In general, all are
less hard than diamond. Moissanite actually has a higher refractive index than diamond, and when presented beside an equivalently sized and cut diamond will show more "fire".
Cultured, synthetic, or "lab-created" gemstones are not
imitations: The bulk mineral and trace coloring elements are the same in
both. For example, diamonds, rubies, sapphires, and emeralds
have been manufactured in labs that possess chemical and physical
characteristics identical to the naturally occurring variety. Synthetic
(lab created) corundum, including ruby and sapphire, is very common and costs much less than the natural stones. Small synthetic diamonds have been manufactured in large quantities as industrial abrasives, although larger gem-quality synthetic diamonds are becoming available in multiple carats.
Whether a gemstone is a natural stone or synthetic, the chemical,
physical, and optical characteristics are the same: They are composed
of the same mineral and are colored by the same trace materials, have the same hardness and density and strength, and show the same color spectrum, refractive index, and birefringence
(if any). Lab-created stones tend to have a more vivid color since
impurities common in natural stones are not present in the synthetic
stone. Synthetics are made free of common naturally occurring impurities
that reduce gem clarity or color unless intentionally added in order to
provide a more drab, natural appearance, or to deceive an assayer.
On the other hand, synthetics often show flaws not seen in natural
stones, such as minute particles of corroded metal from lab trays used
during synthesis.
Types
Some
gemstones are more difficult to synthesize than others and not all
stones are commercially viable to attempt to synthesize. These are the
most common on the market currently.
Synthetic corundum
Synthetic
corundum includes ruby (red variation) and sapphire (other color
variations), both of which are considered highly desired and valued. Ruby was the first gemstone to be synthesized by Auguste Verneuil with his development of the flame-fusion process in 1902.
Synthetic corundum continues to be made typically by flame-fusion as it
is most cost-effective, but can also be produced through flux growth
and hydrothermal growth.
Synthetic beryls
The
most common synthesized beryl is emerald (green). Yellow, red and blue
beryls are possible but much more rare. Synthetic emerald became
possible with the development of the flux growth process and is produced
in this way and well as hydrothermal growth.
Synthetic quartz
Types
of synthetic quartz include citrine, rose quartz, and amethyst. Natural
occurring quartz is not rare, but is nevertheless synthetically
produced as it has practical application outside of aesthetic purposes.
Quartz generates an electric current when under pressure and is used in
watches, clocks, and oscillators.
Synthetic spinel
Synthetic spinel was first produced by accident.
It can be created in any color making it popular to simulate various
natural gemstones. It is created through flux growth and hydrothermal
growth.
Creation process
There are two main categories for creation of these minerals: melt or solution processes.
Verneuil flame fusion process (melt process)
Verneuil furnace
The flame fusion process was the first process used which
successfully created large quantities of synthetic gemstones to be sold
on the market. This remains the most cost effective and common method of creating corundums today.
The flame fusion process is completed in a Verneuil furnace. The
furnace consists of an inverted blowpipe burner which produces an
extremely hot oxyhydrogen flame, a powder dispenser, and a ceramic
pedestal.
A chemical powder which corresponds to the desired gemstone is passed
through this flames. This melts the ingredients which drop on to a plate
and solidify into a crystal called a boule.
For corundum the flame must be 2000 °C. This process takes hours and
yields a crystal with the same properties as its natural counterpart.
To produce corundum, a pure aluminium powder is used with different additives to achieve different colors.
Chromic oxide for ruby
Iron and titanium oxide for blue sapphire
Nickel oxide for yellow sapphire
Nickel, chromium and iron for orange sapphire
Manganese for pink sapphire
Copper for blue-green sapphire
Cobalt for dark blue sapphire
Czochralski process (melt process)
In 1918 this process was developed by J. Czocharalski
and is also referred to as the "crystal pulling" method. In this
process, the required gemstone materials are added to a crucible. A seed
stone is placed into the melt in the crucible. As the gem begins to
crystallize on the seed, the seed is pulled away and the gem continues
to grow. This is used for corundum but is currently the least popular method.
Flux growth (solution process)
The flux growth process was the first process able to synthesize emerald.
Flux growth begins with a crucible which can withstand high heat;
either graphite or platinum which is filled with a molten liquid
referred to as flux.
The specific gem ingredients are added and dissolved in this fluid and
recrystallize to form the desired gemstone.This is a longer process
compared to the flame fusion process and can take two months up to a
year depending on the desired final size.
Hydrothermal growth (solution process)
The
hydrothermal growth process attempts to imitate the natural growth
process of minerals. The required gem materials are sealed in a
container of water and placed under extreme pressure. The water is
heated beyond its boiling point which allows normally insoluble
materials to dissolve. As more material cannot be added once the
container is sealed, in order to create a larger gem the process would
begin with a "seed" stone from a previous batch which the new material
will crystallize on. This process takes a few weeks to complete.
Characteristics
Synthetic
gemstones share chemical and physical properties with natural
gemstones, but there are some slight differences that can be used to
discern synthetic from natural.
These differences are slight and often require microscopy as a tool to
distinguish differences. Undetectable synthetics pose a threat to the
market if they are able to be sold as rare natural gemstones.
Because of this there are certain characteristic gemologists look for.
Each crystal is characteristic to the environment and growth process
under which it was created.
Gemstones created from the flame-fusion process may have
small air bubbles which were trapped inside the boule during formation process
visible banding from formation of the boule
chatter marks which on the surface which appear crack like which are caused from damage during polishing of the gemstone
Gemstones created from flux melt process may have
small cavities which are filled with flux solution
inclusions in the gemstone from crucible used
Gemstones created from hydrothermal growth may have
inclusions from container used
History
Auguste Verneuil – creator of flame-fusion process 1902
Prior to development of synthesising processes the alternatives on
the market to natural gemstones were imitations or fake. In 1837, the
first successful synthesis of ruby occurred.
French chemist Marc Gaudin managed to produce small crystals of ruby
from melting together potassium aluminium sulphate and potassium
chromate through what would later be known as the flux melt process. Following this, another French chemist Fremy was able to grow large quantities of small ruby crystals using a lead flux.
A few years later an alternative to flux melt was developed which
led to the introduction of what was labeled "reconstructed ruby" to the
market. Reconstructed ruby was sold as a process which produced larger
rubies from melting together bits of natural ruby.
In later attempts to recreate this process it was found to not be
possible and is believed reconstructed rubies were most likely created
using a multi-step method of melting of ruby powder.
Auguste Verneuil, a student of Fremy, went on to develop
flame-fusion as an alternative to the flux-melt method. He developed
large furnaces which were able to produce large quantities of corundums
more efficiently and shifted the gemstone market dramatically. This process is still used today and the furnaces have not changed much from the original design. World production of corundum using this method reaches 1000 million carats a year.
List of rare gemstones
Painite
was discovered in 1956 in Ohngaing in Myanmar. The mineral was named in
honor of the British gemologist Arthur Charles Davy Pain. At one point
it was considered the rarest mineral on Earth.
Tanzanite
was discovered in 1967 in Northern Tanzania. With its supply possibly
declining in the next 30 years, this gemstone is considered to be more
rare than a diamond. This type of gemstone receives its vibrant blue
from being heated.
Hibonite
was discovered in 1956 in Madagascar. It was named after the
discoverer, French geologist Paul Hibon. Gem quality hibonite has been
found only in Myanmar.
Red Beryl - discovered in 1940
Red beryl or bixbite was discovered in an area near Beaver, Utah in 1904 and named after the American mineralogist Maynard Bixby.
Jeremejevite was discovered in 1883 in Russia and named after its discoverer, Pawel Wladimirowich Jeremejew (1830–1899).
Chambersite was discovered in 1957 in Chambers County, Texas, US, and named after the deposit's location.
Taaffeite was discovered in 1945. It was named after the discoverer, the Irish gemologist Count Edward Charles Richard Taaffe.
Musgravite was discovered in 1967 in the Musgrave Mountains in South Australia and named for the location.
Black Opal – the rarest type of opal
Black opal
is directly mined in New South Wales, Australia, making it the rarest
type of opal. Having a darker composition, this gemstone can be in a
variety of colours.
Grandidierite
was discovered by Antoine François Alfred Lacroix (1863–1948) in 1902
in Tuléar Province, Madagascar. It was named in honor of the French
naturalist and explorer Alfred Grandidier (1836–1912).
Poudretteite
was discovered in 1965 at the Poudrette Quarry in Canada and named
after the quarry's owners and operators, the Poudrette family.
Serendibite was discovered in Sri Lanka by Sunil Palitha Gunasekera in 1902 and named after Serendib, the old Arabic name for Sri Lanka.
Zektzerite
was discovered by Bart Cannon in 1968 on Kangaroo Ridge near Washington
Pass in Okanogan County, Washington, USA. The mineral was named in
honor of mathematician and geologist Jack Zektzer, who presented the
material for study in 1976.
In popular culture
French singer-songwriter Nolwenn Leroy was inspired by the gemstones for her 2017 album Gemme (meaning gemstone in French) and the single of the same name.
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