Gemology or gemmology is the
science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
dealing with natural and artificial
gemstone
A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
materials. It is a
geoscience
Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres ...
and a branch of
mineralogy
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
. Some
jewelers (and many non-jewelers) are academically trained gemologists and are qualified to identify and evaluate gems.
History
Rudimentary education in gemology for jewellers and gemologists began in the nineteenth century, but the first qualifications were instigated after the National Association of Goldsmiths of Great Britain (NAG) set up a Gemmological Committee for this purpose in 1908. This committee matured into the
Gemmological Association of Great Britain
The Gemmological Association of Great Britain (Gem-A) is an international gemmology education and qualifications body based in the United Kingdom.
History
Gem-A dates back to 1908 when a gemmological committee was established by ''The National A ...
(also known as Gem-A), now an educational charity and accredited awarding body with its courses taught worldwide.
The first US graduate of Gem-A's diploma course, in 1929, was
Robert Shipley, who later established both the
Gemological Institute of America
The Gemological Institute of America (GIA) is a nonprofit institute based in Carlsbad, California. It is dedicated to research and education in the field of gemology and the jewelry arts. Founded in 1931, GIA's mission is to protect buyers and ...
and the
American Gem Society
The American Gem Society (AGS) is a trade association of retail jewelers, independent appraisers, suppliers, and selective industry members, which was founded in 1934 by Robert M. Shipley.
The Society is based in Las Vegas, Nevada, along with th ...
. There are now several professional schools and associations of gemologists and certification programs around the world.
The first gemological laboratory serving the jewelry trade was established in London in 1925, prompted by the influx of the newly developed "cultured pearl" and advances in the synthesis of rubies and sapphires. There are now numerous gem laboratories around the world requiring ever more advanced equipment and experience to identify the new challenges - such as treatments to gems, new synthetics, and other new materials.
Background
It is often difficult to obtain an expert judgement from a neutral laboratory. Analysis and estimation in the gemstone trade usually have to take place on site. Professional gemologists and gemstone buyers use mobile laboratories, which pool all necessary instruments in a travel case. Such so-called travel labs even have their own current supply, which makes them independent from infrastructure. They are also suitable for gemological expeditions.
Gemstones are basically categorized based on their
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...
,
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
,
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
, and other optical properties, such as
pleochroism
Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light.
Backgroun ...
. The physical property of "hardness" is defined by the irregular
Mohs scale of mineral hardness
The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material.
The scale was introduced in 1812 by th ...
.
Gemologists study these factors while valuing or appraising cut and polished gemstones. Gemological microscopic study of the internal structure is used to determine whether a gem is synthetic or natural by revealing natural
fluid inclusions image:Inclumed.gif, 250px, Trapped in a time capsule the same size as the diameter of a human hair, the ore-forming liquid in this inclusion was so hot and contained so much dissolved solids that when it cooled, crystals of halite, sylvite, gypsum, ...
or partially melted
exogenous
In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, the fact of being influenced within a system.
Economics
In an economic model, an exogeno ...
crystals that are evidence of heat treatment to enhance color.
The spectroscopic analysis of cut gemstones also allows a gemologist to understand the atomic structure and identify its origin, which is a major factor in valuing a gemstone. For example, a
ruby
A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sa ...
from Burma will have definite internal and optical activity variance from a Thai ruby.
When the gemstones are in a rough state, the gemologist studies the external structure; the host rock and mineral association; and natural and polished color. Initially, the stone is identified by its color, refractive index, optical character, specific gravity, and examination of internal characteristics under magnification.
Gemological instruments
Gemologists use a variety of tools and equipment which allow for the accurate tests to be performed in order to identify a gemstone by its specific characteristics and properties.
![KA52KRS_1_m](https://upload.wikimedia.org/wikipedia/commons/1/15/KA52KRS_1_m.jpg)
These include:
* Corrected 10×
loupe
A loupe ( ) is a simple, small magnification device used to see small details more closely. They generally have higher magnification than a magnifying glass, and are designed to be held or worn close to the eye. A loupe does not have an attached h ...
* Microscope
* Refractometer
** Polarising filter
** Magnifying eyepiece
** Contact liquid for RI (refractive index) up to 1.81
* Polariscope
** Optic figure sphere
*
Dichroscope
A dichroscope is a pocket instrument used in the field of gemology, and can be used to test transparent gemstones (crystals). Experienced gemologists, observing the pleochroism of some gems, can successfully detect gemstones from other artificial s ...
* Spectroscope (handheld or desktop)
* Penlight
* Tweezers
* Stone cloth
* Color filter
* Immersion cell
* Ultraviolet lamp
General identification of gems
![Gem](https://upload.wikimedia.org/wikipedia/commons/5/5e/Gem.pebbles.800pix.jpg)
Gem identification is basically a process of elimination. Gemstones of similar color undergo non-destructive optical testing until there is only one possible identity.
Any single test is nearly always only indicative. For example: The
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
of
ruby
A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sa ...
is 4.00,
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
is 3.15–4.20, and
cubic zirconia
Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconi ...
is 5.6–5.9 . So one can easily tell the difference between cubic zirconia and the other two; however, there is overlap between ruby and glass.
As with all naturally occurring materials, no two gems are identical. The geological environment they are created in influences the overall process so that although the basics can be identified, the presence of chemical "impurities", and substitutions along with structural imperfections create "individuals".
Identification by refractive index
One test to determine the gem's identity is to measure the refraction of light in the gem. Essentially, when light passes from one medium to another, it bends. Blue light bends more than red light. How much the light bends will vary depending on the gem mineral.
Every material has a
critical angle
Critical angle may refer to:
*Critical angle (optics), the angle of incidence above which total internal reflection occurs
*Critical angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference lin ...
, above which point light is reflected back internally. This can be measured and thus used to determine the gem's identity. Typically this is measured using a
refractometer
A refractometer is a laboratory or field device for the measurement of an Refractive index, index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index ...
, although it is possible to measure it using a microscope.
Identification by specific gravity
Specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
, also known as relative density, varies depending upon the chemical composition and crystal structure type. Heavy liquids with a known specific gravity are used to test loose gemstones.
Specific gravity is measured by comparing the weight of the gem in air with the weight of the gem suspended in water.
Identification by spectroscopy
This method uses a similar principle to how a
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
works to separate white light into its component colors. A gemological
spectroscope
An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...
is employed to analyze the selective absorption of light in the gem material. Coloring agents or chromophores show bands in the spectroscope and indicate which element is responsible for the gem's color.
Identification by inclusions
Inclusions can help gemologists to determine whether or not a gemstone is natural, synthetic or treated (i.e. fracture-filled or heated).
Identification by flaws and striations
![Curved_Striations_in_Synthetic_Color-Change_Sapphire](https://upload.wikimedia.org/wikipedia/commons/9/99/Curved_Striations_in_Synthetic_Color-Change_Sapphire.jpg)
During the
Verneuil process
The Verneuil method (or Verneuil process or Verneuil technique), also called flame fusion, was the first commercially successful method of manufacturing synthetic gemstones, developed in the late 1883 by the French chemist Auguste Verneuil. It ...
for synthesizing gems, a fine crushed material is heated at extremely high temperatures. The powdered gem mineral is then melted (or a metallic mixture directly burned in an oxygen flame) the residue of which then drips through a furnace onto a boule. The boule where the
corundum
Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the pres ...
or
spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals.
Properties
S ...
cools down and crystallizes, spins and thus causes the curved striations, which are diagnostic for a lab-created gem: Natural corundum does not show curved striations.
Likewise, natural stones, particularly
beryl
Beryl ( ) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several mete ...
minerals, show small flaws – short planar cracks where the direction of the crystalline orientation in the gem abruptly changes. The natural formation of gemstones tends to layer the minerals in regular crystalline sheets, whereas many synthetically produced gems have an amorphous structure, like glass. Synthetics made by the Verneuil process either do not show flaws at all, or if any flaws are present, show curvy, undulating surfaces rather than flat ones.
Institutes, laboratories, schools, and publications
Institutes
*
American Gem Society
The American Gem Society (AGS) is a trade association of retail jewelers, independent appraisers, suppliers, and selective industry members, which was founded in 1934 by Robert M. Shipley.
The Society is based in Las Vegas, Nevada, along with th ...
— AGS
*
Asian Institute of Gemological Sciences
The Asian Institute of Gemological Sciences (AIGS) is a private gemological school and gemological laboratory based in Bangkok, Thailand.
History
The AIGS was founded in 1978 and was Thailand's first educational facility devoted to the study o ...
— AIGS
*
Canadian Gemmological Association
The Canadian Gemmological Association (CGA) is a Canada-wide professional organization which sets standards in the practice of gemology. It is a non-profit, educational organization, which provides a forum for Canadian gemmologists to meet and sh ...
— CGA
*
Canadian Institute of Gemmology — CIG
*
Gemological Science International
Gemological Science International, or GSI, is an independent gemological organization that is one of the largest gemological entities in the world, with offices in four continents.
Founded in New York City in 2005 by Mark Gershburg and Debbie Az ...
— GSI
*
Gemmological Association of Australia — GAA
*
Gemmological Association of Great Britain
The Gemmological Association of Great Britain (Gem-A) is an international gemmology education and qualifications body based in the United Kingdom.
History
Gem-A dates back to 1908 when a gemmological committee was established by ''The National A ...
— Gem-A
*
Gemological Institute of America
The Gemological Institute of America (GIA) is a nonprofit institute based in Carlsbad, California. It is dedicated to research and education in the field of gemology and the jewelry arts. Founded in 1931, GIA's mission is to protect buyers and ...
— GIA
*
Institut National de Gemmologie - ING
*
Hoge Raad voor Diamant
The Antwerp World Diamond Centre (AWDC) is a public/private corporation, officially representing and coordinating the Antwerp diamond sector. It is located in heart of Antwerp in the Hoveniersstraat. The chief executive officer of AWDC is Ari Epste ...
— HRD
*
International Gemological Institute
International Gemological Institute (IGI) is a diamond, colored stone and jewelry certification organization. IGI is headquartered in Antwerp and has offices in New York City, Hong Kong, Mumbai, Bangkok, Tokyo, Dubai, Tel Aviv, Toronto, Los Ang ...
— IGI
*
Italian Gemmological Institute — IGI
* Institute of Gem Trading — IGT
*
Gemmological Institute of India
Gemmological Institute of India is a gemmology training school in Mumbai, India.
Description
The Gemological Institute of India (GII) is a non-profit school in Mumbai that conducts courses on gemmology. It was founded in April 1971 by the Gem a ...
— GII
*
Center of Gemological of Indonesia — COG
*
Swiss Gemmological Institute — SSEF
Commercial laboratories
*
American Gemological Laboratories — AGL
*
European Gemological Laboratory
European, or Europeans, or Europeneans, may refer to:
In general
* ''European'', an adjective referring to something of, from, or related to Europe
** Ethnic groups in Europe
** Demographics of Europe
** European cuisine, the cuisines of Europe ...
— EGL
*
Gübelin Gem Lab — GGL
*
Laboratoire français de gemmologie — LFG
*
Professional gemstone testing laboratory — PGTL
*
Himalaya gem testing laboratory
The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
— HGTL
*
Universal Gemological Laboratories — GCI
Publications
* ''
The Journal of Gemmology''
* ''
Gems & Gemology
''Gems & Gemology'' is a quarterly scientific journal published by the Gemological Institute of America. Each issue is devoted to research on diamonds, gemstones, and pearls. Topics include geographic sources, imitations and synthetics, treatment ...
''
Footnotes
References
{{Authority control
Mineralogy
Gemological_laboratories