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Encyclopedia > Gemstone
Gemology and Jewelry Portal

A gemstone, gem or also called precious or semi-precious stone is a highly attractive and valuable piece of mineral, which — when cut and polished — is used in jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are strictly speaking not minerals, but are still applied in jewelry and adornments, and are therefore often considered a gemstone as well. Some minerals that are too soft to be generally applied in jewelry may still be considered a gemstone because of their remarkable color, lustre or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Gemstone may refer to: Gemstones, rocks or minerals often used for jewelry, ornamentation, or technological application. ... Image File history File links No higher resolution available. ... A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. ... Jewelry (the American spelling; spelled jewellery in Commonwealth English) consists of ornamental devices worn by persons, typically made with gems and precious metals. ... For other uses, see Rock (disambiguation). ... Lapis lazuli, also known as just lapis, is a stone with one of the longest traditions of being considered a gem, with a history stretching back to 7000 BC in Mehrgarh in the Indian subcontinent, situated in between modern day Afghanistan, and Pakistan. ... Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, halogens as well... This article or section is in need of attention from an expert on the subject. ... A sample of jet Jet is a geological material that is not considered a mineral in the true sense of the word, but rather, a mineraloid derived from decaying wood under extreme pressure, thus organic in origin. ... Color is an important part of the visual arts. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ...

A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm long (1.6 inches).
A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm long (1.6 inches).

Contents

Download high resolution version (800x825, 129 KB)A selection of gem pebbles: made by tumbling rough rock with abrasive, in a rotating drum. ... Download high resolution version (800x825, 129 KB)A selection of gem pebbles: made by tumbling rough rock with abrasive, in a rotating drum. ...

Characteristics and classification

Gemstones are described by gemologists using technical specifications. First, what is it made of, or its chemical composition. Diamonds for example are made of carbon (C) and rubies of aluminium oxide (Al2O3). Next, many gems are crystals which are classified by 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. Gemology (gemmology outside the United States) is the science, art and profession of identifying and evaluating gemstones. ... Technical terminology is the specialised vocabulary of a profession or of some other activity to which a group of people dedicate significant parts of their lives (for instance, hobbies or a particular segment of industry). ... The chemical composition of a substance refers to the elements of which the substance is composed. ... This article is about the gemstone. ... For other uses, see Carbon (disambiguation). ... Ruby is a red gemstone, a variety of the mineral corundum in which the color is caused mainly by chromium. ... “Aluminum” redirects here. ... A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of point groups. ... The cubic crystal system is a crystal system where the unit cell is in the shape of a cube. ... In crystallography, the rhombohedral (or trigonal) crystal system is one of the 7 lattice point groups. ... In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ...


Gems 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. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl. This article does not cite any references or sources. ... Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. ... For other uses, see Sapphire (disambiguation). ... This article or section does not cite its references or sources. ... Aquamarine (Lat. ... Bixbite (also known as red beryl, red emerald, or scarlet emerald) is a red variety of beryl (emerald), Be3(Al,Mn)2Si6O18. ... Beryl var. ... Morganite is a pink coloured gem quality beryl, orange/yellow morganite is sometimes found also, it turns pink upon high temperature treatment. ... Three varieties of beryl: Morganite, Aquamarine, and Heliodor The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. ...


Gems have refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and lustre. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum. The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... Dispersion of a light beam in a prism. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... This article or section does not cite any references or sources. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For fractures in geologic formations, see Rock fracture. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... Pleochroism is an optical phenomenon in which grains of a rock appear to be different colors when observed at different angles,under a petrographic microscope. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the division of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Luminescence is light not generated by high temperatures alone. ... A materials absorption spectrum shows the fraction of incident electromagnetic radiation absorbed by the material over a range of frequencies. ...


Material or flaws within a stone may be present as inclusions. The gem may occur in certain locations, called the "occurrence." In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. ...


Value of Gemstones, Past and Present

Jewelry made with gem amber
Jewelry made with gem amber

The diamond is a gemstone which has its value determined in a different way than most or even all other gemstones. Traditionally the diamond was valued mostly for its physical properties such as hardness and brilliance, not unlike any other (colored) gemstone, and since a diamond was not particularly rare, [2], other (colored) gemstones such as a sapphire or a ruby were valued higher than a diamond for a long time. Although the large diamond finds in South Africa created an even larger supply of diamonds, its trade in the 20th century also became strongly regulated by a single organization: De Beers. [3]. Both their monopoly of the market and their continuous marketing campaign in the last 50-75 years have greatly influenced the perceived value of a diamond, unlike that of any other (colored) gemstone. Amber pendants. ... Amber pendants. ... De Beers, founded in South Africa by Cecil Rhodes, comprises companies involved in rough diamond exploration, diamond mining and diamond trading. ...


The remainder of this article deals with colored gemstones and we refer to the diamonds section for a discussion about diamonds. This article is about the gemstone. ...


A valuable (colored) gemstone is prized especially for its great beauty, rarity or aesthetics. Although color plays a very important role in determining the value of a gemstone, many other factors influence its price as well: market supply (think of the fluctuations of Tanzanite prices), rarity (Red Beryl), popularity of a stone, market mechanisms etc. Tanzanite is the blue/purple variety of the mineral zoisite discovered in the Meralani Hills of northern Tanzania in 1967, near the city of Arusha. ... Bixbite (also known as red beryl, red emerald, or scarlet emerald) is a red variety of beryl (emerald), Be3(Al,Mn)2Si6O18. ...


General 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, and asteria (star effects). The Greeks for example greatly valued asteria in gemstones, which were regarded as a powerful love charm, and Hellen of Troy was known to have worn star-corundum. [4] An optical phenomenon is any observable event which results from the interaction of light and matter. ... Asteria in Greek mythology can refer to: // In Greek mythology, Asteria was the sixth Amazon killed by Heracles when he came for Hippolytes girdle. ... Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. ...


A factor in determining the value of a gemstone is called water. Water is an archaic term that refers to the combination of color and transparency in gemstones; used hierarchically: first water (gem of the finest water), second water, third water, byewater. [5]


Historically gemstones were classified into precious stones and semi-precious stones. Because such a definition can change over time, vary per culture and can depend on so many factors, it has always been a difficult matter to determine what constitutes precious stones. [6]


Aside from the diamond, ruby, sapphire, emerald, the pearl (strictly speaking not a gemstone) was also considered to be precious as well as the opal. [6]. At least at the beginning of the 20th century these stones were considered precious more often than not because of their beauty. 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 the Aquamarine, Peridot, Cat's eye have had their days of increased popularity and hence value [6], much like present day. This article is about the gemstone. ... This article does not cite any references or sources. ... For other uses, see Sapphire (disambiguation). ... This article or section does not cite its references or sources. ... Freshadama grade cultured freshwater pearls. ... For other OPAL articles, see Opal (disambiguation). ... For other uses, see Amethyst (disambiguation). ... Aquamarine (Lat. ... This article is about the mineral. ... There are a number of things named Cats Eye: The reflective property of certain gems: see Chatoyancy Cats Eye (film) is a 1985 horror film based on works by Stephen King Cats Eye (novel) is a 1989 Booker Prize nominated work by Margaret Atwood Cats eyes...


Nowadays such a distinction is no longer made by the trade. [5] 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 meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and bixbite. Andalusite-cordierite schist (Large brown crystals are Andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. ... Axinite is a brown to violet-brown, or reddish-brown bladed mineral composed of calcium aluminum boro-silicate, (Ca,Fe,Mn)3Al2BO3Si4O12OH. Axinite is pyroelectric and piezoelectric. ... Cassiterite is a tin oxide mineral, SnO2. ... Clinohumite is an uncommon member of the humite group of minerals, a magnesium silicate according to the chemical formula (Mg,Fe)7(SiO4)3(F,OH)2. ... Bixbite (also known as red beryl, red emerald, or scarlet emerald) is a red variety of beryl (emerald), Be3(Al,Mn)2Si6O18. ...


Gems prices can fluctuate heavily (such as those of Tanzanite over the years) or can be quite stable (such as those of diamonds). In general per carat prices of larger stones are higher than those of smaller stones, but popularity of certain sized stone can jade prices considerably. Typically per carat prices can range from $5/carat for a normal Amethyst to 20.000-50.000 for a collector's 3 carat pidgeon-blood almost "perfect" Ruby.


Grading

In the last two decades there has been a proliferation of certification, not only for diamonds but for gemstones as well. There are five [5] major laboratories which grade and provide reports on gemstones.

  • Gemological Institute of America (GIA)
  • American Gemological Society (AGS) is not as widely recognized nor as old as the GIA but garners a high reputation.
  • American Gem Trade Laboratory which is part of the American Gem Trade Association (AGTA) the largest trade organization of jewelers and dealers of colored stones
  • American Gemological Laboratories (AGL) which was recently taken over by "Collector's Universe" a NASDAQ listed company which specializes in certification of many collectables such as coins and stamps
  • European Gemological Laboratory (EGL).

Although certification can provide certainty and clarity, each laboratory has its own methodology to evaluate gemstones; grading experience is different and depending on the cert required each lab approaches these issues differently. Consequently 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 concludes that it is heat treated. [5] Countries of origin has sometimes been difficult to find agreement on due to the constant discovery of new locations. Gem labs need time to study them. Moreover determining a "country of origin" does not have the exact scientific methods at its disposal as other aspects of a gem (such as cut, clarity etc.) [7] The Gemological Institute of America, or GIA, is a non-profit institute dedicated to research and education in the field of gemology. ... The American Gem Society (AGS) is a trade association of professional gemologists founded in 1934 by Robert M. Shipley, who also founded the Gemological Institute of America (GIA). ... NASDAQ in Times Square, New York City. ...


Gem dealers are fully aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible cert [5]. One such example is to make use of the differences in "Country of Origin": a sapphire from Kashmir (celebrated for its cornflower blue color) commands four times the price of the same stone from Ceylon and twice the price if the stone were from Burma. [8]


Cutting and polishing

A few gemstones are used as gems in the crystal or other form in which they are found. Most however, are cut and polished for usage as gemstones. The two main classifications are stones cut as smooth, dome shaped stones called cabochons, and stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at planned angles. Moonstone cabochons in a jewellers window A cabochon or cabouchon is a gemstone which has been shaped and polished as opposed to facetted. ... A faceting machine is broadly defined as any device that allows the user to place and polish facets onto a mineral specimen. ... Facets are flat faces on geometric shapes. ...


Stones which are opaque such as opal, turquoise, 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.[9] For other OPAL articles, see Opal (disambiguation). ... For other uses, see Turquoise (disambiguation). ... Variscite AlPO4·2H2O, hydrated aluminium phosphate, is a relatively rare phosphate mineral. ...


Gems which are transparent are normally faceted, a method which 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. 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. Special equipment, a faceting machine, is used to hold the stone onto a flat lap for cutting and polishing the flat facets.[10] Rarely, some cutters use special curved laps to cut and polish curved facets. See also list of optical topics. ... A faceting machine is broadly defined as any device that allows the user to place and polish facets onto a mineral specimen. ...


Gemstone color

Color is the most obvious and attractive feature of gemstones. The color of any material is due to the nature of light itself. Daylight, often called white light, is actually a mixture of different colors of light. When light passes through a material, some of the light may be absorbed, while the rest passes through. The part that isn't absorbed reaches our eye as white light minus the absorbed colors. A ruby appears red because it absorbs all the other colors of white light - blue, yellow, green, etc. - except red.


The same material can exhibit different colors. For example ruby and sapphire have the same chemical composition (both are corundum) but exhibit different colors. Even the same 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". Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. ...


This difference in color is based on the atomic structure of the stone. Although the different stones formally have the same chemical composition, they are not exactly the same. Every now and then an atom is replaced by a completely different atom (and this could be as few as one in a million atoms). These so called impurities are sufficient to absorb certain colors and leave the other colors unaffected. Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound. ...


As an example: beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If you add manganese instead of chromium, beryl becomes pink morganite. With iron, it becomes aquamarine. Morganite is a pink coloured gem quality beryl, orange/yellow morganite is sometimes found also, it turns pink upon high temperature treatment. ... Aquamarine (Lat. ...


Several gemstone treatments actually make use of the fact that these impurities can be "manipulated", thus changing the color of the gem.


Treatments applied to gemstones

Treble clef with gemstones
Treble clef with gemstones

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 and accepted in practice 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.[11] Image File history File linksMetadata Download high resolution version (394x800, 200 KB) Beschreibung Violinschluessel aus Edelsteinen und Halbedelsteinen (gemstones)von Claudia von Aponte, Austria. ... Image File history File linksMetadata Download high resolution version (394x800, 200 KB) Beschreibung Violinschluessel aus Edelsteinen und Halbedelsteinen (gemstones)von Claudia von Aponte, Austria. ...


Heat

Heat can improve gemstone color or clarity. Most Citrine is made by heating amethyst, and partial heating with a strong gradient results in ametrine - a stone partly amethyst and partly citrine. Much Aquamarine is heat treated to remove yellow tones, change the green color into the more desirable blue or enhance its existing blue color to a purer blue. [12] 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. Citrine Citrine, also called citrine quartz is an amber-colored gemstone. ... Ametrine Ametrine (or trystine) is a naturally occurring variety of quartz. ...


Radiation

Most 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. Some improperly handled gems which do not pass through normal legal channels may have a slight residual radiation, though strong requirements on imported stones are in place to ensure public safety. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color. Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. ... Irradiation is the process by which an item is exposed to radiation. ...


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

Fracture filling has been in use with different gemstones such as Diamonds, Emeralds, Sapphires. More recently (in 2006) "Glass Filled Rubies" received a lot of publicity. Rubies over 10 carat (2 g), particularly sold in the Asian market with large fractures were filled with Lead Glass, thus dramatically improving the appearance of larger Rubies in particular. Such treatments are still fairly easy to detect.


Synthetic and artificial gemstones

Some gemstones are manufactured to imitate other gemstones. For example, cubic zirconia is a synthetic diamond simulant composed of zirconium oxide. The imitations copy the look and color of the real stone but possess neither their chemical nor physical characteristics. However, true synthetic gemstones are not necessarily imitation. For example, diamonds, ruby, sapphires and emeralds have been manufactured in labs, which possess very nearly identical chemical and physical characteristics to the naturally occurring variety. Synthetic corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones. Smaller synthetic diamonds have been manufactured in large quantities as industrial abrasives for many years. Only recently, larger synthetic diamonds of gemstone quality, especially of the colored variety, have been manufactured. A round brilliant-cut cubic zirconia Cubic zirconia (or CZ), the cubic crystalline form of zirconium dioxide (ZrO2), is a mineral that is widely synthesized for use as a diamond simulant. ... Due to its low cost and close visual likeness to diamond, cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... This article does not cite any references or sources. ... For other uses, see Sapphire (disambiguation). ... This article or section does not cite its references or sources. ... Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. ... A colourless synthetic diamond produced via chemical vapour deposition Synthetic diamond is diamond produced through chemical or physical processes in a factory. ... An abrasive is a material, often a mineral, that is used to shape or finish (see metal polishing and wood finishing) a workpiece through rubbing which leads to part of the workpiece being worn away. ... A colourless synthetic diamond produced via chemical vapour deposition Synthetic diamond is diamond produced through chemical or physical processes in a factory. ...


See also

There are over 130 species of minerals that have been cut into gemstones with 50 species in common use. ... Much like their real-life counterparts, fictional gemstones are things of beauty, admiration, or curses. ...

Notes

  1. ^ The Oxford Dictionary Online and Webster Online Dictionary
  2. ^ Williams, Gardner (1905). The Diamond Mines of South Africa Vol.I and II. Buck & Company. 
  3. ^ Gregory, Theodore (1962). Ernest Oppenheimer. Oxford University Press. 
  4. ^ Burnham, S.M. (1868). Precious Stones in Nature, Art and Literature. Bradlee Whidden.  Page 251
  5. ^ a b c d e Secrets of the Gem Trade; The Connoisseur's Guide to Precious Gemstones Richard W Wise, Brunswick House Press, Lenox, Massachutes., 2003 URL: Secrets of the Gem Trade, Official Website (Has several chapters online)
  6. ^ a b c Church, A.H. (Professor at Royal Academy of Arts in London) (1905). Precious Stones considered in their scientific and artistic relations. His Majesty's Stationary Office, Wyman & Sons.  Chapter 1, Page 9: Definition of Precious Stones URL: Definition of Precious Stones
  7. ^ [Rapaport report of ICA Gemstone Conferene in Dubai]
  8. ^ [Richard Wise Blog on Christie's sale of Padparadscha Sapphire]
  9. ^ Introduction to Lapidary by Pansy D. Kraus
  10. ^ Faceting For Amateurs by Glen and Martha Vargas
  11. ^ Gemstone Enhancement: History, Science and State of the Art by Kurt Nassau
  12. ^ Nassau, Kurt (1994). Gem Enhancements. Butterworth Heineman. 

External links


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