Gemstone

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Group of precious and semiprecious stones--both uncut and faceted--including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster. Cardinal gems.png
Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster.

A gemstone (also called a 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 jewelry or other adornments. [1] [2] [3] However, certain rocks (such as lapis lazuli and opal) and occasionally organic materials that are not minerals (such as amber, jet, and 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 or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.

Contents

Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter; a diamond cutter is called a diamantaire.

Characteristics and classification

A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm (1.6 in) long. Gem.pebbles.800pix.labelled.jpg
A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm (1.6 in) long.

The traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. In modern use the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious. [4] This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the Mohs scale. Other stones are classified by their color, translucency, and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called tsavorite can be far more valuable than a mid-quality emerald. [5] Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not necessarily the case.

In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al
2
O
3
). Many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example, diamonds, which have a cubic crystal system, are often found as octahedrons.

Gemstones are classified into different groups, species, and varieties. [6] [ self-published source? ] For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow) and morganite (pink), which are all varieties of the mineral species beryl.

Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.

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". [7] Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency. [8]

Value

Spanish emerald and gold pendant at Victoria and Albert Museum Spanish jewellery-Gold and emerald pendant at VAM-01.jpg
Spanish emerald and gold pendant at Victoria and Albert Museum
Enamelled gold, amethyst, and pearl pendant, about 1880, Pasquale Novissimo (1844-1914), V&A Museum number M.36-1928 Pendant.jpg
Enamelled gold, amethyst, and pearl pendant, about 1880, Pasquale Novissimo (1844–1914), V&A Museum number M.36-1928

Gemstones have no universally accepted grading system. Diamonds are graded[ by whom? ] using a system developed by the Gemological Institute of America (GIA) in the early 1950s. Historically, all gemstones were graded using the naked eye. The GIA system included a major innovation: the introduction of 10x magnification as the standard for grading clarity. Other gemstones are still graded using the naked eye (assuming 20/20 vision). [9]

A mnemonic device, the "four Cs" (color, cut, clarity, and carats), has been introduced[ by whom? ] to help describe the factors used to grade a diamond. [10] 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 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 was supposed to have worn star-corundum. [11] [ failed verification ]

Aside from the diamond, the ruby, sapphire, emerald, pearl (not, strictly speaking, a gemstone), and opal [12] have also been considered[ by whom? ] to be precious. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a "precious stone" as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat's eye (cymophane) have been popular and hence been regarded as precious.

Today the gemstone trade no longer makes such a distinction. [13] 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. [14]

Rare or unusual gemstones, generally understood to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and red beryl. [15]

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.[ citation needed ] Diamond value can change based on location, time, and on the evaluations of diamond vendors. [16] [ failed verification ]

Proponents of energy medicine also value gemstones on the basis of alleged healing powers. [17]

Grading

There are a number of laboratories which grade and provide reports on gemstones. [13]

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. [13] 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.). [19]

Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate. [13]

Cutting and polishing

Raw sapphire stones stored in a rural commercial cutting plant in Thailand. Gemstones raw.JPG
Raw sapphire stones stored in a rural commercial cutting plant in Thailand.
A diamond cutter in Amsterdam in the Netherlands in 2012 Diamond cutter. Amsterdam. 2012.jpg
A diamond cutter in Amsterdam in the Netherlands in 2012

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 cabochons, and stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at exact angles.

Stones which are opaque or semi-opaque such as opal, turquoise, variscite, etc. are commonly cut as cabochons. These gems are designed to show the stone's color 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. [20]

Gems that are transparent are normally faceted, a method that shows the optical properties of the stone's interior to its best advantage by maximizing reflected light which is perceived by the viewer as sparkle. There are many commonly used shapes for faceted stones. The facets must be cut at the proper angles, which varies depending on the optical properties of the gem. If the angles are too steep or too shallow, the light will pass through and not be reflected back toward the viewer. The faceting machine is used to hold the stone onto a flat lap for cutting and polishing the flat facets. [21] Rarely, some cutters use special curved laps to cut and polish curved facets.

Colors

Nearly 300 variations of diamond color exhibited at the Aurora display at the Natural History Museum in London. Aurora Pyramid of Hope.jpg
Nearly 300 variations of diamond color exhibited at the Aurora display at the Natural History Museum in London.

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) 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". [22]

This difference in color is based on the atomic structure of the stone. Although the different stones formally have the same chemical composition and structure, they are not exactly the same. Every now and then an atom is replaced by a completely different atom, sometimes as few as one in a million atoms. These so-called impurities are sufficient to absorb certain colors and leave the other colors unaffected.

For example, beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If manganese is added instead of chromium, beryl becomes pink morganite. With iron, it becomes aquamarine.

Some gemstone treatments make use of the fact that these impurities can be "manipulated", thus changing the color of the gem. [6]

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. [23]

Heat

Heat can either improve or spoil gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in "ametrine" – a stone partly amethyst and partly citrine. Aquamarine is often heated to remove yellow tones, or to change green colors into the more desirable blue, or enhance its existing blue color to a deeper blue. [24]

Nearly all tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue / purple color. [25] A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity.

When jewelry containing diamonds is heated (for repairs) the diamond should be protected with boric acid; otherwise, the diamond (which is pure carbon) could be burned on the surface or even burned completely up. When jewelry containing sapphires or rubies is heated, those stones should not be coated with 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 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 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 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, 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. [26] Imitation or simulated stones are chemically different from the natural stone, but may appear quite similar to it; they can be more easily manufactured synthetic gemstones of a different mineral (spinel), glass, plastic, resins, or other compounds.

Examples of simulated or imitation stones include cubic zirconia, composed of zirconium oxide, synthetic moissanite, and un-colored, synthetic corrundum or spinels; all of which are diamond simulants. The simulants imitate the look and color of the real stone but possess neither their chemical nor physical characteristics. In general, all are less hard than diamond. Moissanite actually has a higher refractive index than diamond, and when presented beside an equivalently sized and cut diamond will show more "fire".

Cultured, synthetic, or "lab-created" gemstones are not imitations: The bulk mineral and trace coloring elements are the same in both. For example, diamonds, rubies, sapphires, and emeralds have been manufactured in labs that possess chemical and physical characteristics identical to the naturally occurring variety. Synthetic (lab created) corrundum, including ruby and sapphire, is very common and costs much less than the natural stones. Small synthetic diamonds have been manufactured in large quantities as industrial abrasives, although larger gem-quality synthetic diamonds are becoming available in multiple carats. [27]

Whether a gemstone is a natural stone or synthetic, the chemical, physical, and optical characteristics are the same: They are composed of the same mineral and are colored by the same trace materials, have the same hardness and density and strength, and show the same color spectrum, refractive index, and birefringence (if any). Lab-created stones tend to have a more vivid color since impurities common in natural stones are not present in the synthetic stone. Synthetics are made free of common naturally occurring impurities that reduce gem clarity or color unless intentionally added in order to provide a more drab, natural appearance, or to deceive an assayer.[ citation needed ] 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

See also

Related Research Articles

Corundum Oxide mineral

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 also a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. Corundum has two primary gem varieties: ruby and sapphire. Rubies are red due to the presence of chromium, and sapphires exhibit a range of colors depending on what transition metal is present. A rare type of sapphire, padparadscha sapphire, is pink-orange.

Emerald Green gemstone, a beryl variety

Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium and/or sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.

Sapphire Gem variety of corundum

Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al2O3) with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. Red corundum stones also occur but are called rubies not sapphires. Pink-colored corundum may be classified either as ruby or sapphire depending on locale. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of special-purpose solid-state electronics such as integrated circuits and GaN-based blue LEDs. Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years.

Ruby Variety of corundum, mineral, gemstone

A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum. Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond. The word ruby comes from ruber, Latin for red. The color of a ruby is due to the element chromium.

Chrysoberyl Mineral or gemstone of beryllium aluminate

The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones, although they both contain beryllium. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8).

Gemology Science dealing with natural and artificial gemstone materials

Gemology or gemmology is the science dealing with natural and artificial gemstone materials. It is a geoscience and a branch of mineralogy. Some jewelers are academically trained gemologists and are qualified to identify and evaluate gems.

Tanzanite Blue to purple variety of the mineral zoisite

Tanzanite is the blue and violet variety of the mineral zoisite, caused by small amounts of vanadium. Tanzanite belongs to the epidote mineral group. Tanzanite is only found in Tanzania, in a very small mining area near the Mererani Hills.

Diamond cut Style or design guide

A diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape, but the symmetry, proportioning and polish of a diamond. The cut of a diamond greatly affects a diamond's brilliance; this means if it is cut poorly, it will be less luminous.

Diamond clarity

Diamond clarity is the quality of diamonds that relates to the existence and visual appearance of internal characteristics of a diamond called inclusions, and surface defects, called blemishes. Clarity is one of the four Cs of diamond grading, the others being carat, color, and cut.

Diamond color

A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink diamonds or blue diamonds can be dramatically more valuable. Of all colored diamonds, red diamonds are the rarest. The Aurora Pyramid of Hope displays a spectacular array of naturally colored diamonds, including red diamonds.

Diamond simulant diamond-like object which is not a diamond

A diamond simulant, diamond imitation or imitation diamond is an object or material with gemological characteristics similar to those of a diamond. Simulants are distinct from synthetic diamonds, which are actual diamonds having the same material properties as natural diamonds. Enhanced diamonds are also excluded from this definition. A diamond simulant may be artificial, natural, or in some cases a combination thereof. While their material properties depart markedly from those of diamond, simulants have certain desired characteristics—such as dispersion and hardness—which lend themselves to imitation. Trained gemologists with appropriate equipment are able to distinguish natural and synthetic diamonds from all diamond simulants, primarily by visual inspection.

Gemological Institute of America Research institute in Carlsbad, California

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. Founded in 1931, GIA's mission is to protect all buyers and sellers of gemstones by setting and maintaining the standards used to evaluate gemstone quality. The institute does so through research, gem identification and diamond grading services and a variety of educational programs. Through its world-renowned library and subject experts, GIA acts as a resource of gem and jewelry information for the trade, the public and worldwide media outlets.

Tairus

Tairus is a synthetic gemstone manufacturer. It was formed in 1989 as part of Mikhail Gorbachev's perestroika initiative to establish a joint venture between the Russian Academy of Sciences and Tairus Created Gems Co Ltd. of Bangkok, Thailand. Today Tairus is a major supplier of hydrothermally grown gemstones to the jewellery industry. Later, Tairus became a privately held enterprise, operating out of its Bangkok distribution hub under the trade name Tairus, owned by Tairus Created Gems Co Ltd. of Bangkok, Thailand.

The Asian Institute of Gemological Sciences (AIGS) is a private gemological school and gemological laboratory based in Bangkok, Thailand. The AIGS was founded in 1978 and was Thailand's first educational facility devoted to the study of gemstones. The school and the laboratory are located in the Jewelry Trade Center, on Silom Road, in the heart of the gem and jewellery district of Bangkok.

Diamond (gemstone) Gemstone

Diamond is one of the best-known and most sought-after gemstones. They have been used as decorative items since ancient times.

Shelby Gem Factory American artificial gemstone manufacturer

The Shelby Gem Factory, also known as ICT Incorporated, was a Michigan company that manufactured artificial gemstones through proprietary processes. The factory made more varieties of man-made gemstones than any other in the world. It grew artificial gems and gem simulants, including synthetic ruby and sapphire and simulated diamonds, citrine, topaz, and other birthstone substitutes, and mounted them in gold or silver jewelry.

Blue diamond

Blue diamond is a type of diamond which exhibits all of the same inherent properties of the mineral except with the additional element of blue color in the stone. They are colored blue by trace amounts of boron that contaminate the crystalline lattice structure. Blue diamonds belong to a subcategory of diamonds called fancy color diamonds, the generic name for diamonds that exhibit intense color.

Lotus Gemology

Lotus Gemology is a gemology laboratory located in Bangkok, Thailand. It was founded in 2014 by Richard W. Hughes & Wimon Manorotkul and their daughter, E. Billie Hughes. Their idea was that, while precious stones were articles of great beauty, the lab reports issued by gem labs better resembled blood tests from a doctor than a celebration of that beauty. Thus they set about creating lab reports that were both scientifically accurate and aesthetically beautiful. Lotus Gemology's lab report covers are color coded. Gold reports are reserved for gems that are completely untreated, while silver reports are for gems that have been subjected to industry-standard treatments. Black reports are reserved for heavily treated and man-made gems. This consumer-friendly approach is unique in the industry.

References

  1. "Gemstone". Lexico. Oxford University Press.
  2. Webster Online Dictionary Archived 2007-06-03 at the Wayback Machine
  3. Alden, Nancy (2009). Simply Gemstones: Designs for Creating Beaded Gemstone Jewelry. New York, NY: Random House. p. 136. ISBN   978-0-307-45135-4.
  4. Bauer, Max (1968). Precious Stones. Dover Publications. p. 2. ISBN   9780486219103.
  5. Wise, R. W., 2006, Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones, Brunswick House Pr, pp. 3–8 ISBN   0-9728223-8-0
  6. 1 2 Frangoulis, George (18 April 2015). GEM HUNTER. Lulu.com. ISBN   9781329075634.[ self-published source ]
  7. AskOxford.com Concise Oxford English dictionary online.[ full citation needed ]
  8. Desirable diamonds: The world's most famous gem. by Sarah Todd.[ full citation needed ]
  9. Wise, R. W., 2006, Secrets of The Gem Trade, The Connoisseur's Guide To Precious Gemstones, Brunswick House Pr, p.36 ISBN   0-9728223-8-0
  10. Wise, R. W., 2006, Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones, Brunswick House Pr, p. 15
  11. Burnham, S.M. (1868). Precious Stones in Nature, Art and Literature. Bradlee Whidden. Page 251 URL: Helen of Troy and star corundum Archived 2010-10-13 at the Wayback Machine
  12. Church, A.H. (1905). "Definition of Precious Stones". Precious Stones considered in their scientific and artistic relations. His Majesty's Stationery Office, Wyman & Sons. p. 11. Archived from the original on 2007-09-29 via Farlang.com.
  13. 1 2 3 4 Secrets of the Gem Trade; The Connoisseur's Guide to Precious Gemstones, Richard W Wise, Brunswick House Press, Lenox, Massachusetts., 2003
  14. "5 Most Precious Stones". HowStuffWorks.com. 2009-11-09. Archived from the original on 2014-11-06.
  15. "A complete guide to Gemstones". Jewellery Monthly. 2015-04-02. Archived from the original on 2017-08-28.
  16. "Artificial treatment of gemstones". Dictionary of Gems and Gemology . Berlin, Heidelberg: Springer Berlin Heidelberg. 2009. pp.  50. doi:10.1007/978-3-540-72816-0_1308. ISBN   9783540727958.
  17. Katz, Michael (2005). Gemstone Energy Medicine: Healing Body, Mind and Spirit. Natural Healing Press. ISBN   9780924700248 . Retrieved 2020-04-06.
  18. "The Gem and Jewelry Institute of Thailand (Public Organization)". Bangkok Post.
  19. "Rapaport report of ICA Gemstone Conference in Dubai". Diamonds.net. 2007-05-16. Archived from the original on 2011-07-26. Retrieved 2010-07-30.
  20. Kraus, Pansy D. (2007). Introduction to Lapidary . Krause Publications. ISBN   9780801972669.
  21. Vargas, Glenn; Vargas, Martha (2002). Faceting For Amateurs. ISBN   9780917646096.
  22. "Padparadscha Sapphires: 10 Tips On Judging The Rare Gem". The Natural Sapphire Company Blog. 2015-04-06. Retrieved 2018-01-19.
  23. Gemstone Enhancement: History, Science and State of the Art by Kurt Nassau
  24. Nassau, Kurt (1994). Gem Enhancements. Butterworth Heineman.
  25. "Tanzanite heating – the science". Archived from the original on 20 June 2016.
  26. Jewelers' circular-keystone: JCK. Chilton Company. 1994.[ full citation needed ]
  27. "New process promises bigger, better diamond crystals". Carnegie Institution for Science. Archived from the original on 1 December 2010. Retrieved 7 January 2011.
  28. Folkard, Claire; Freshfield, Jackie; Masson, Carla; Dimery, Rob (12 December 2017). Guinness World Records 2005. Guinness World Records Limited. ISBN   9780851121925.
  29. Hainschwang, Thomas; Notari, Franck; Massi, Laurent; Armbruster, Thomas; Rondeau, Benjamin; Fritsch, Emmanuel; Nagashima, Mariko (Summer 2010). "Hibonite: A New Gem Mineral" (PDF). Gems & Gemology. 46 (2): 135–138. doi:10.5741/GEMS.46.2.135.