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A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
crystal A crystal or crystalline solid is a solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformatio ...

crystal
which, in cut and polished form, is used to make
jewelry Jewellery or jewelry consists of decorative items worn for personal adornment 150px, The principal adornment of these girls from the Bundu tribe in Sierra Leone is the adornment of bodies and faces with markings produced by the smearing on by ...

jewelry
or other
adornment 150px, The principal adornment of these girls from the Bundu tribe in Sierra Leone is the adornment of bodies and faces with markings produced by the smearing on by the fingers of a substance called "wojeh," composed of white clay and animal fat. ...

adornment
s. However, certain
rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proc ...
(such as
lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism up ...

lapis lazuli
and
opal Opal is a hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

opal
) and occasionally
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or ...
materials that are not minerals (such as
amber Amber is fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was ...

amber
, jet, and
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle (mollusc), mantle) of a living animal shell, shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pe ...

pearl
) are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their
luster Lustre or Luster may refer to: Places * Luster, Norway, a municipality in Vestlandet, Norway ** Luster (village), a village in the municipality of Luster * Lustre, Montana, an unincorporated community in the United States Entertainment * Luste ...
or other physical properties that have
aesthetic value Aesthetics, or esthetics (), is a branch of philosophy that deals with the nature of beauty and taste (sociology), taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines subjective and s ...
. Rarity and notoriety are other characteristics that lend value to gemstones. Apart from jewelry, from earliest antiquity
engraved gem An engraved gem, frequently referred to as an intaglio, is a small and usually semi-precious gemstone that has been carved, in the Western tradition normally with images or inscriptions only on one face. The engraving of gemstones was a major lux ...
s and
hardstone carving Hardstone carving is a general term in art history and archaeology for the artistic carving of predominantly semi-precious stones (but also of gemstones), such as jade, rock crystal (clear quartz), agate, onyx, jasper, serpentinite, or carnelian, ...
s, such as cups, were major luxury art forms. A gem maker is called a
lapidary Lapidary (from the Latin ) is the practice of shaping Rock (geology), stone, minerals, or gemstones into decorative items such as cabochons, engraved gems (including cameo (carving), cameos), and faceted designs. A person who practices lapidary ...
or
gemcutter Lapidary (from the Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repub ...
; a
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At Standard conditions for temperature and pressure, room temperature and pressure, another solid form of ...

diamond
cutter is called a
diamantaire A diamantaire (''French origin'') is a gem-quality diamond manufacturer or producer, master diamond cutting, diamond cutter, and graduate gemologist specialized in diamonds. Such individuals demonstrate considerable expertise in different types of ...
.


Characteristics and classification

The traditional classification in the West, which goes back to the
ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of History of Greece, Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, antiquity ( AD 600). This era was ...
, begins with a distinction between ''precious'' and ''semi-precious''; similar distinctions are made in other cultures. In modern use, the precious stones are
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At Standard conditions for temperature and pressure, room temperature and pressure, another solid form of ...

diamond
,
ruby A ruby is a pink to blood-red coloured gemstone A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or othe ...

ruby
,
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
and
emerald Emerald is a gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with ...

emerald
, 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 In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions are ...
with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale Ordinal data is a categorical, statistical data type where the variables have natural, ordered categories and the distances between the categories are not known. These data e ...
. Other stones are classified by their color,
translucency In the field of optics Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its ...
, and hardness. The traditional distinction does not necessarily reflect modern values; for example, while
garnet Garnets () are a group of silicate mineral Silicate minerals are rock-forming mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science c ...

garnet
s are relatively inexpensive, a green garnet called
tsavorite Tsavorite or tsavolite is a variety of the garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age The Bronze Age is a prehistoric Periodization, period that was characterized by the use of bronze, in ...
can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in
art history
art history
and
archaeology Archaeology or archeology is the study of human activity through the recovery and analysis Analysis is the process of breaking a complexity, complex topic or Substance theory, substance into smaller parts in order to gain a better underst ...
is
hardstone Hardstone is a non-scientific term, mostly encountered in the decorative arts ] The decorative arts are arts or crafts whose object is the design A design is a plan or specification for the construction of an object or system or for the imple ...
. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not necessarily the case. In modern times gemstones are identified by gemology, gemologists, who describe gems and their characteristics using
technical terminology Jargon is the specialized terminology Terminology is a general word for the group of specialized words or meanings relating to a particular field, and also the study of such terms and their use. This is also known as terminology science. Terms a ...
specific to the field of
gemology Gemology or gemmology is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable ex ...
. The first characteristic a gemologist uses to identify a gemstone is its
chemical composition {{Unreferenced, date=December 2017 Chemical composition refers to identity and number of the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an el ...
. For example,
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At Standard conditions for temperature and pressure, room temperature and pressure, another solid form of ...

diamond
s are made of
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
(C) and rubies of
aluminium oxide Aluminium oxide is a chemical compound of aluminium and oxygen with the chemical formula 23. It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as aluminium(III) oxide. It is ...

aluminium oxide
(). Many gems are crystals which are classified by their
crystal system In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "col ...
such as
cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system 200px, A network ...
or
trigonal A triangle is a polygon with three Edge (geometry), edges and three Vertex (geometry), vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC. In Euclidean geometry, any ...
or
monoclinic In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' " ...

monoclinic
. Another term used is
habit A habit (or wont as a humorous and formal term) is a routine of behavior Behavior (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of t ...
, the form the gem is usually found in. For example, diamonds, which have a cubic crystal system, are often found as
octahedron In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces, twelve edges, and six vertices. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral tri ...

octahedron
s. Gemstones are classified into different ''groups'', ''species'', and ''varieties''. For example, ruby is the red variety of the species
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
, while any other color of corundum is considered sapphire. Other examples are the
emerald Emerald is a gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with ...

emerald
(green),
aquamarine Aquamarine may refer to: * Aquamarine (color) Aquamarine is a color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the ...
(blue),
red beryl
red beryl
(red),
goshenite Beryl ( ) is a mineral composed of beryllium aluminium Silicate minerals#Cyclosilicates, cyclosilicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and #Aquamarine and maxixe, aquamarine. Naturally occur ...
(colorless),
heliodor
heliodor
(yellow), and
morganite
morganite
(pink), which are all varieties of the mineral species
beryl Beryl ( ) is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which i ...

beryl
. Gems are characterized in terms of
refractive index In optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or ...

refractive index
,
dispersion Dispersion may refer to: Economics and finance *Dispersion (finance), a measure for the statistical distribution of portfolio returns *Price dispersion, a variation in prices across sellers of the same item *Wage dispersion, the amount of variation ...
,
specific gravity Relative density, or specific gravity, is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemon ...
,
hardness Hardness (antonym: softness) is a measure of the resistance to localized plastic deformation In engineering, deformation refers to the change in size or shape of an object. ''Displacements'' are the ''absolute'' change in position of a point ...
,
cleavage Cleavage may refer to: Science * Cleavage (crystal), in mineralogy and materials science, a process of splitting a crystal * Cleavage (geology), the foliation perpendicular to stress as a result of ductile deformation * Cleavage (embryo), in embr ...
,
fracture Fracture is the separation of an object or material into two or more pieces under the action of stress (physics), stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the ...

fracture
and luster. They may exhibit
pleochroism Pleochroism (from Greek wikt:πλείων#Ancient Greek, πλέων, ''pléōn'', "more" and wikt:χρώμα#Ancient Greek, χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at d ...
or
double refraction Birefringence is the optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...

double refraction
. They may have
luminescence Luminescence is spontaneous emission of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usually defined ...

luminescence
and a distinctive
absorption spectrum Absorption may refer to: Chemistry and biology *Absorption (chemistry) In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: th ...
. Material or flaws within a stone may be present as inclusions. 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 In the gemstone trade, first water means "highest quality". The Diamond clarity, clarity of diamonds is assessed by their translucence; the more like water, the higher the quality. The 1753 edition of Chambers' Encyclopedia states "The first water ...
", while "second" or "third water" gems are those of a lesser transparency.


Value

Gemstones have no universally accepted grading system. Diamonds are graded using a system developed by the
Gemological Institute of America The Gemological Institute of America (GIA) is a nonprofit institute dedicated to research and education in the field of gemology and the jewelry arts and based in Carlsbad, California Carlsbad is a coastal city in the North County (San Diego ar ...
(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 A mnemonic (, the first "m" is not pronounced) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory Memory is the faculty of the brain by which data or informat ...
, 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. The ideal 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 Optical phenomena are any observable events that result from the interaction of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the huma ...
within the stone such as color zoning (the uneven distribution of coloring within a gem) and asteria (star effects). Ancient Greeks, for example, greatly valued asteria gemstones, which they regarded as powerful love charms, and
Helen of Troy In Greek mythology Greek mythology is the body of myth Myth is a folklore genre Folklore is the expressive body of culture shared by a particular group of people; it encompasses the tradition A tradition is a belief A bel ...

Helen of Troy
was supposed to have worn star-
corundum Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
. Page 251 URL
Helen of Troy and star corundum
Aside from the
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At Standard conditions for temperature and pressure, room temperature and pressure, another solid form of ...

diamond
,
ruby A ruby is a pink to blood-red coloured gemstone A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or othe ...

ruby
,
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
, and
emerald Emerald is a gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with ...

emerald
, the
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle (mollusc), mantle) of a living animal shell, shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pe ...

pearl
(not, strictly speaking, a gemstone) and
opal Opal is a hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

opal
have also been considered to be precious. Up to the discoveries of bulk
amethyst Amethyst is a violet (color), violet variety of quartz. The name comes from the Koine Greek αμέθυστος ''amethystos'' from α- ''a-'', "not" and μεθύσκω (Ancient Greek) / μεθώ (Modern Greek), "intoxicate", a reference to ...

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 Aquamarine may refer to: * Aquamarine (color) Aquamarine is a color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the ...
,
peridot Peridot ( ), sometimes called chrysolite, is gem A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or othe ...

peridot
and cat's eye (
cymophane
cymophane
) have been popular and hence been regarded as precious. 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 Andalusite is an aluminium Silicate minerals, nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétehrie, who thought it came from Andalusia. It soon became clear that it was a locality error, and t ...

andalusite
, ,
cassiterite Cassiterite is a tin Tin is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that al ...

cassiterite
,
clinohumite Clinohumite is an uncommon member of the Humite (mineral group), humite group, a magnesium silicate according to the chemical formula (magnesium, Mg, iron, Fe)9(silicon, Sioxygen, O4)4(fluorine, F,Ohydrogen, H)2. The formula can be thought of as ...

clinohumite
and . 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. Diamond value can change based on location, time, and on the evaluations of diamond vendors. Proponents of
energy medicine Energy medicine is a branch of alternative medicine Alternative medicine is any practice that aims to achieve the healing effects of medicine, but which lacks biological plausibility and is Argument from ignorance, untested, Pseudoscience ...
also value gemstones on the basis of alleged
healing With physical damage or disease suffered by an organism, healing involves the repair of living tissue(s), organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ s ...

healing
powers.


Grading

There are a number of laboratories which grade and provide reports on gemstones.'' Secrets of the Gem Trade; The Connoisseur's Guide to Precious Gemstones'', Richard W Wise, Brunswick House Press, Lenox, Massachusetts., 2003 *
Gemological Institute of America The Gemological Institute of America (GIA) is a nonprofit institute dedicated to research and education in the field of gemology and the jewelry arts and based in Carlsbad, California Carlsbad is a coastal city in the North County (San Diego ar ...
(GIA), the main provider of education services and diamond grading reports *
International Gemological Institute International Gemological Institute (IGI) is a diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure In crystallography Crystallography is the experimental science of determining the arrangem ...
(IGI), independent laboratory for grading and evaluation of diamonds, jewelry, and colored stones *
Hoge Raad Voor Diamant The Antwerp World Diamond Centre (AWDC) is a public/private corporation, officially representing and coordinating the Antwerp Antwerp (; nl, Antwerpen ; french: Anvers ) is a city in Belgium and the capital of Antwerp (province), Antwerp prov ...
(HRD Antwerp), The Diamond High Council, Belgium is one of Europe's oldest laboratories; its main stakeholder is the Antwerp World Diamond Centre * American Gemological Society (AGS) is not as widely recognized nor as old as the GIA * 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 *
Asian Institute of Gemological Sciences The Asian Institute of Gemological Sciences (AIGS) is a private gemological school and gemological laboratory based in Bangkok Bangkok is the capital and most populous city of Thailand. It is known in Thai language, Thai as Krung Thep Maha Nakho ...
(AIGS), the oldest gemological institute in South East Asia, involved in gemological education and gem testing * 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 * Institute for Gems and Gold Research of VINAGEMS (Vietnam), founded by Dr. Van Long Pham 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.


Cutting and polishing

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 stones cut as smooth, dome-shaped stones called
cabochon A cabochon (, from Middle French Middle French (french: moyen français) is a historical division of the French language French ( or ) is a Romance language of the Indo-European family The Indo-European languages are a language fam ...

cabochon
s, and stones which are cut with a
faceting machine A faceting machine is broadly defined as any device that allows the user to place and polish facets onto a mineral specimen. Machines can range in sophistication from primitive jamb-peg machines to highly refined, and highly expensive, commercial ...
by polishing small flat windows called
facet Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline so ...
s at regular intervals at exact angles. Stones which are opaque or semi-opaque such as
opal Opal is a hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

opal
,
turquoise Turquoise is an opaque Opacity or opaque may refer to: * Impediments to (especially, visible) light: ** Opacities, absorption coefficients ** Opacity (optics), property or degree of blocking the transmission of light * Metaphors derived from li ...

turquoise
,
variscite Variscite is a hydrated aluminium phosphate mineral (·2 H2O). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper Coppe ...

variscite
, etc. are commonly cut as cabochons. These gems are designed to show the stone's color or surface properties as in opal and star sapphires. 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 Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entitie ...
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

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 the other colors of white light while reflecting the 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 Corundum is a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directio ...

corundum
) but exhibit different colors because of impurities. 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 Impurities are chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
are sufficient to absorb certain colors and leave the other colors unaffected. For example,
beryl Beryl ( ) is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which i ...

beryl
, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If
manganese Manganese is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical e ...

manganese
is added instead of
chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

chromium
, beryl becomes pink . With iron, it becomes
aquamarine Aquamarine may refer to: * Aquamarine (color) Aquamarine is a color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the ...
. 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. 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.


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 Amethyst is a violet (color), violet variety of quartz. The name comes from the Koine Greek αμέθυστος ''amethystos'' from α- ''a-'', "not" and μεθύσκω (Ancient Greek) / μεθώ (Modern Greek), "intoxicate", a reference to ...

amethyst
, and partial heating with a strong gradient results in " ametrine" – a stone partly amethyst and partly citrine.
Aquamarine Aquamarine may refer to: * Aquamarine (color) Aquamarine is a color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the ...
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 Tanzanite is the blue and violet variety of the mineral zoisite (a calcium aluminium hydroxyl sorosilicate), caused by small amounts of vanadium Vanadium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodi ...

tanzanite
is heated at low temperatures to remove brown undertones and give a more desirable blue / purple color. A considerable portion of all
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
and
ruby A ruby is a pink to blood-red coloured gemstone A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or othe ...

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 Boric acid, also called hydrogen borate, boracic acid, and orthoboric acid is a weak, monobasic Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is ...

boric acid
; otherwise, the diamond (which is pure carbon) could be burned on the surface or even burned completely up. When jewelry containing
sapphires Sapphire is a precious gemstone A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or other adornments. H ...
or
rubies A ruby is a pink-ish red to blood-red colored gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaki ...
is heated, those stones should not be coated with boracic 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).


Radiation

Virtually all blue topaz, both the lighter and the darker blue shades such as "London" blue, has been
irradiated Irradiation is the process by which an object is exposed to radiation upThe international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for unshielded humans. Radiation, in general, exists throughout na ...

irradiated
to change the color from white to blue. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color. Diamonds are
irradiated Irradiation is the process by which an object is exposed to radiation upThe international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for unshielded humans. Radiation, in general, exists throughout na ...
to produce fancy-color diamonds (which can occur naturally, though rarely in gem quality).


Waxing/oiling

Emeralds containing natural fissures are sometimes filled with
wax Waxes are a diverse class of organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prope ...
or
oil An oil is any nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound ...

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

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.


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 Spinel () is the magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of ma ...
), glass, plastic, resins, or other compounds. Examples of simulated or imitation stones include
cubic zirconia Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a ...
, composed of
zirconium Zirconium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

zirconium
oxide, synthetic
moissanite Moissanite is naturally occurring silicon carbide Silicon carbide (SiC), also known as carborundum (), is a semiconductor containing silicon and carbon. It occurs in nature as the extremely rare mineral moissanite. Synthetic SiC powder has bee ...

moissanite
, and un-colored, synthetic
corundum Corundum is a crystal A crystal or crystalline solid is a solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance th ...
or
spinel Spinel () is the magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of ma ...
s; 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,
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At Standard conditions for temperature and pressure, room temperature and pressure, another solid form of ...

diamond
s,
rubies A ruby is a pink-ish red to blood-red colored gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaki ...

rubies
,
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
s, and
emerald Emerald is a gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with ...

emerald
s have been manufactured in labs that possess chemical and physical characteristics identical to the naturally occurring variety. Synthetic (lab created)
corundum Corundum is a crystal A crystal or crystalline solid is a solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance th ...
, including ruby and sapphire, is very common and costs much less than the natural stones. Small
synthetic diamond Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis As a topic ...

synthetic diamond
s have been manufactured in large quantities as industrial
abrasive An abrasive is a material, often a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs n ...
s, 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 In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
and are colored by the same trace materials, have the same
hardness Hardness (antonym: softness) is a measure of the resistance to localized plastic deformation In engineering, deformation refers to the change in size or shape of an object. ''Displacements'' are the ''absolute'' change in position of a point ...
and
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
and
strength Physical strength *Physical strength, as in people or animals *Hysterical strength, extreme strength occurring when people are in life-and-death situations *Superhuman strength, great physical strength far above human capability *A common attrib ...
, and show the same
color spectrum Laser beams with visible spectrum The visible spectrum is the portion of the electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition ...

color spectrum
,
refractive index In optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or ...

refractive index
, and
birefringence Birefringence is the property of a material having a that depends on the and propagation direction of . These optically materials are said to be birefringent (or birefractive). The birefringence is often quantified as the maximum difference b ...

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.


List of rare gemstones

*
Painite Painite is a very rare borate mineral. It was first found in Myanmar Myanmar (; my, မြန်မာ ) or Burma ( my, ဗမာ ), officially the Republic of the Union of Myanmar, is a country in Southeast Asia. Myanmar is bordered by ...
was discovered in 1956 in Ohngaing in Myanmar. The mineral was named in honor of the British gemologist Arthur Charles Davy Pain. In 2005, painite was described by the Guinness Book of World Records as the rarest gem mineral on earth. * Hibonite was discovered in 1956 in Madagascar. It was named after the discoverer the French geologist Paul Hibon. Gem quality hibonite has been found only in Myanmar. * 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. * 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.


See also

* Assembled gem * Gemology * List of gemstone species * List of gemstones *Luminous gemstones


References


External links

{{Authority control Gemstones, Jewellery components Materials Mineralogy Minerals, * Stone objects