A large number of stones used in jewellery are semi-precious. The most importance ones are here:
Agate: Agate is the most familiar of the sub-verities of chalcedony. It is commonly composed of alternating layers of difference thickness, colour & porosity that tend to parallel the walls of the rock cavity in which it was deposited. The natural colours being 1) in intercalated bands distinctly marked from each other- called “banded agate”, the difference in the bands being due to degrees of transparency and colour and to inclusions of milky layers alternating with layers of quartz, jasper, cornelian or onyx. 2) In cloud-like, moss-like or dendrite form. It available in many parts of the world & was used extensively in Egypt and Rome, in ornamental pieces and in jewellery such as beads & brooches; in the Middle Ages it was worn as an amulet or talisman. Also used for wall peaces, in watches & in aquarium.
Almandine:It’s never occurs pure in nature but for convenience, gems near the end of the almandine- pyrope solid solution series are called almandine. It’s a variety of garnet that is transparent and commonly deep crimson with tinges of purple. Mainly the colour range is from red-violet to dark brownish-red. It, colour may resemble that ruby.
Alexandrite:A variety of chrysoberyl like cat’s eye. This is a very attractive but costly stone. Due to the presence of oxide of chromium, it appears dull grass-green by day-light (which is rich in blue rays), but by electric light is appears yellowish or reddish-yellow and by soft candle-light (which is rich in red rays) it appears reddish. Best alexandrite comes from Russia, Burma (Myanmar), USA, Madagascar, Brazil and Ceylon.
Amazonite:Amazonite is also called “Amazon Stone”, because of Amazon River; where formerly green coloured stones found. Amazonite is a light green to bluish-green coloured with white mottled flecks. It is a non-transparent or translucent stone. It’s mostly found in Brazil, United States, Zimbabwe, Australia, Russia, Namibia and Colorado.
Amber:Amber is a one of organic gems which produce by biological process, whether animal or vegetable. An amorphous translucent or opaque fossilized natural resin from an extinct variety of pine tree submerged under the sea some 50 to 60 million years ago. It is light in weight, warm to the touch, very brittle and electrified when rubbed. Its colour covers a wide range, usually from yellow to honey, brown or reddish-brown; it some times has a dusty, friable reddish-brown, light brown or gray crust due to alteration. It is found in variously shaped nodules. Mainly amber is find from Baltic States and the Dominical Republic. Other sources of amber are Russia, Kaliningrad, Lithuania, Estonia, Latvia, Poland, Denmark, Myanmar (Burma), Lebanon, Sicily, Mexico, Romania, Canada, England and Norway.
Amethyst: A transparent and crystalline variety of Quartz, usually deep purple to pale-purple or bluish violet, reddish-mauve, reddish-violet and gray-mauve coloured. Amethyst is found from Brazil, Madagascar, Zambia, Uruguay, India, Burma (Myanmar), Canada, Mexico, Namibia, Russia, Sri Lanka and United States. The best stones are faceted; others are tumbled & beads used in jewellery. When natural amethysts (not the variety from Madagascar) are heated, the colour changes to pale yellow; when the heat is increased, it changes to dark yellow or reddish-brown and when increased further, to milky white. Some Brazilian amethysts when heated change colour to green. There are some amethysts that lose some colour in daylight. The original colour can be restoring by X-ray radiation. Amethyst is also used as a hilling-stone in Fang-Sue.
Apatite:The name is derived from Greek word “apate”, means to deceive. Basically apatite is known for its asparagus-green colour but also available in other wide varieties of colours like pink, blue, greenish-blue, violet, yellow and colour-less too. Deposits of apatite are in India, Burma, Brazil, Kenya, Madagascar, Mexico, Sri Lanka, Norway, South Africa and United States.
Aquamarine:It’s a variety of beryl that is transparent and of various shades of blue and blue-green. Aquamarine is so named because of its seawater colour. In Latin it’s called “water of sea”. The stones are diachronic, brittle and sensitive to pressure. Most aquamarine comes from pegmatites of Brazil, where crystals weighing several kilos have been found. Other deposits are in India, Soviet Union, Madagascar, United States, Afghanistan, China, Kenya, Mozambique, Namibia, Nigeria, Zambia and Zimbabwe. The largest aquamarine was found in 1910 in Marambaya, Minas Gerais (Brazil). Rich blue stones several carats in weight are among the most valuable of secondary gems. They are worth a lot more, for instance, than blue topaz of similar characteristic. Pale or green stones are less valuable. Because of its cool and attractive colour, aquamarine is favorite gem of all modern designers.
Aventurine:The name aventurine is applied to an ornamental material consisting mainly of quartz. The granular appearance, the possible presence of distinct green fibers, and its particular translucence are the most distinctive characteristics. It’s available in soft-green, silvery, yellow, reddish-brown, greenish-brown, orange and bluish-green. Aventurine comes mostly from India, Soviet Union, Brazil, Tanzania and Australia. Very modest, when as is usually the case, the material is whitish to grayish or dull green, and the workmanship is of a low level. But expertly fashioned, bright green stones are more valuable. Aventurine used for jewellery and other ornamental pieces from many centuries.
Azurite:Azurite is a blue copper carbonate, so-called because of its intense azure-blue colour. It occurs at the same localities as malachite and although less abundant, the two minerals are almost invariably associated. Azurite in places occurs in well-formed monoclinic crystals. It has a vitreous luster. Exceptional dark blue –almost black crystals have come from Namibia, Morocco, Australia, Chile, Mexico, Russia and United States.
Beryl:Beryl is a mineral with several gem varieties covering a wide range of colours. Deep green beryl are called Emerald (one of the most valuable of all gems), blue – aquamarine and other colours called precious beryl. The name beryl comes from India and has always been associated with the gemstone. Beryl is also the most abundant mineral containing beryllium and is the chief source of this rare light element with many important industrial uses. Main colours found in beryl are emerald-green, sea-green (Emerald), blue (Aquamarine), raspberry-red (Bixbite), all shades between lemon-yellow & golden-yellow (Golden Beryl), colourless (Goshenite), light yellow-green (Heliodor), soft pink to violet (Morganite or Pink Beryl) and pale-green, bluish-green, yellowish-green (Green Beryl). Deposits of beryl are in India, United States, Brazil, Namibia, Madagascar, Nigeria, Sri Lanka, Zimbabwe, China, Canada, Mexico, Russia and Afghanistan.
Blood stone:Blood-stone is an opaque, dark-green or blackish-green chalcedony with red spots. An old name still used in Europe is heliotrope. The most important deposits are in India, also found in Australia, Brazil, China and United States.
Calcite:Calcite is a very common mineral that occurs in a wide variety of colours, texture and forms. It is the predominant or only mineral of limestone, marble and onyx marble, all used as ornamental stones.
Carnelian:Is probably named after the colour of the kornel cherry because of its colour. Carnelian is variety of chalcedony that is usually flesh-red, but also ranges from yellowish-red to reddish-brown translucent or opaque. The colour is intensified by heating. The stone is sometimes mottled by flecks of the matrix. It is hard and tough, and so is often carved in intaglio from all the seal, or used as beads. Deposits are found from India, Brazil and Uruguay.
Chalcedony:This is the name given to the microcrystalline varieties of quartz. However because of colour variation or banding, sub varieties of chalcedony are given special names. Specifically, chalcedony is a honey-yellow to gray, translucent or opaque stones with waxy luster. But for ornamental purpose, the types that have been variously coloured by small quantities of other elements are usually used. These colours are brownish-yellow, red, black, green, black & white, Gray & white, yellow, brownish-red and almost all shades of these colours with milky look. Sometimes in several colours blended into each other. It is commonly found with agate as in Uruguay & Brazil; it also found in India, Madagascar, Namibia, Zimbabwe, Sri Lanka and California.
Chrysoberyl:The name chrysoberyl is derived from Greek chryso (golden). The colour varies of
chrysoberyl is from golden-yellow and brown to yellowish-green or bluish-green, also available in green and pale yellow. The dark green variety is called alexandrite. A colourless variety is rare. Chrisoberyl is mainly found from Brazil, Sri Lanka and Madagascar.
Chrysoprase:It is considered the most valuable stone in chalcedony group. By the presence of a nickel compound, chrysoprase is an apple-green coloured. It used as cabochons for necklaces and ornamental objects. In earlier centuries, it was used as a luxurious decorative stone for interior decoration. Chrysoprase mainly comes from India, Germany, Soviet Union, United States, Canada, Brazil, Australia, Kazakhstan, Madagascar, Zimbabwe, South Africa, Tanzania and California.
Citrine:Pale to dark yellow, lemon yellow and golden-yellow quartz. It is commonly mistaken for and sometimes sold as the more valuable topaz. Natural citrines are rare. Most commercial citrines are hear-treated amethyst or smoky quartz. Brazilian amethyst turns light yellow at 470 degrees C. Some smoky quartzes turn into citrine colour already at about 200 degrees C. Almost all heat-treated citrine have a reddish tint. The natural citrines are mostly pale yellow. Deposits of natural colour citrine are found in Brazil, Madagascar, United States, Argentina, Burma, Namibia, Russia, Scotland and Spain.
Corundum:The hardest mineral other than diamond. The name corundum has its origin in India and probably referred to ruby. Its found in two varieties, 1) common corundum, which is impure, coarse, opaque and granular, and used as an abrasive; 2) transparent corundum, which included three of the most important precious stones, Ruby, Sapphire & Pukhraj. Corundum exhibits a wide range of colours like: blue, green, pink, yellow, golden etc.; and such stones are properly termed sapphires preceded by the appropriate colour, except that the red variety is called Ruby. Common corundum is a relatively abundant mineral, and because it is surpassed only by diamond in hardness, tones are mined each year for use as an abrasive. This superior hardness also contributes greatly to the value of this mineral as a gem. Ruby, sapphire & pukhraj have been highly priced since ancient times, and much lore and legend are associated with them. Corundum is mostly found from India, Burma, Thailand, Sri Lanka, Tanzania, Cambodia, Australia, United States & Malawi.
Dolomite:It’s a colourless, transparent mineral, sometimes also available in pastel colours.
Fluorite:It has a vitreous luster; colour distribution is often zonal or spotty. Mostly found in Germany, Argentina, England, Burma, France, Namibia, Austria, Illinois and Switzerland.
Garnet:This is a group of differently coloured minerals with similar crystal structure and related chemical composition, some varieties being so close as to be difficult to differentiate. The traditional colour is dark red, but the stones are found in many colours & shades, depending on the chemical composition. The main representatives are grossularite (hessonite, rosolite), pyrope (rhodolite), almandine, andradite, spessartite & uvarovite. Garnets were mostly used in Indian traditional ornaments, Anglo-Saxon jewellery, and Victorian jewellery; also used by Egyptians, Greeks, Romans and Celts. Deposits of garnet are found in India, Brazil, Burma (Myanmar), China, Madagascar, Sri Lanka, United States, Namibia, South Africa and Tanzania.
Iolite:It is the Greek-blue or sapphire-blue gem variety of the mineral known as Cordierite. It is also called Dichroite. Water sapphire is misleading name early applied to the gem. It has greasy vitreous luster. Mostly found in Burma, Brazil, India, Sri Lanka, Madagascar and United States.
Ivory:Originally ivory is a hard, creamy-white, opaque dentine that forms the tusks of elephants. Today it is also the teeth of hippopotamus, narwhal, walrus, wild boar and fossilized mammoth. It is translucent when cut in thin sheets. It is initially white but ages with a yellow or brownish patina, and is mark with delicate horizontal graining. Different ivories show different colours under ultraviolet light. Because it is relatively soft and easily worked, ivory has been a favored medium for carving since the earliest civilization. It has long been used for jewellery in the form of finger rings, pendants, brooches, beads, bangles, buckles, pins etc... and for ornamental purpose. Because of ivory is a dentine, it confused with bone. Since 1989, there has been a worldwide ban on any trade in elephant’s ivory. Most ivories come from India, Africa, Burma and Indonesia.
Jade:Two distinct and unrelated species, jadeite & nephrite called Jade. Differentiation between jadeite & nephrite is based on properties, but the term jade is used as a description of both. Jade is available in green & other colours too. The gem which had been known from 7,000 years was used for arms and tools, Chinese used for making weapons and ritual ornaments because of exceptional toughness. The green variety of jade, nephrite - Chinese called “yu”, and also known as axe-stone; found from Burma, Australia, New Zealand, Brazil, Mexico, China, Central America, Canada, Zimbabwe, Russia, Taiwan Alaska and Poland.
Jasper:In earliest history jasper is known as “Spotted stone”. It is usually consider as chalcedony or agate, some scientists put it in a group because of its grainy structure. Mostly used for ornamental purpose. It is nearly opaque with a dull luster and usually admixed with other material. Jasper is available in red, white, brown, yellow & other colours. Deposits of jasper are found from India, Australia, Canada, Brazil, Madagascar, Russia, Uruguay, Kazakhstan and United States.
Lapis (Lazuli):Lapis lazuli is a gem material consisting of a complex mixture of several minerals. In addition to the feldspathoid mineral group, plus calcite, pyrite, and often small amount of augite, hornblende and mica, therefore, lapis is not a mineral, it’s a rock. It is a translucent or opaque. It is a strong but lively blue, sometimes with a violet tint. In lapis contains grayish, off-white or golden patches. Lapis lazuli is sensitive to strong pressure and high temperatures, hot baths, acids and alkalis. Rings should be taken off during household work. It mostly found from Afghanistan, Russia, Chile, Myanmar, Canada, Colorado, California, Pakistan and Angola.
Malachite: It also called “Kidney Stone” because it was supposed to cure kidney ailments if applied to the side of the body
Moonstone:Is a most important and translucent variety of feldspar, shows a blue-whitish, pinkish-white, peach-white or yellowish-white opalescence, which glides over the surface when moon-stone is cut as cabochon. The name moonstone because if put in a moonlight it’s look like a snow-peace. It is available in India, Myanmar, Brazil, Sri Lanka and Madagascar.
Mother-of-Pearl:Mother-of-pearl is an organic gem material, is an inner material of a mollusk shell. In jewellery mother of pearl of the pearl mollusk is mostly used. Basic colour of mother-of-pearl is basically white with rainbow; it is naturally dark in mother of pearl from Tahiti pearl. The mother-of-pearl of pearl mollusk is called sea opal, because of a resemblance to the colour effects seen in opal. Mother-of-pearl used as costume jewellery and also supporting character for diamond and gold jewellery.
Opal:The name opal is derived from Indian- Sanskrit word for stone. A gem opal is usually characterized by a flashing mixture of prismatic colours of delicate huge when light falls upon the surface. It dose not have a crystalline form, but is amorphous, gelatinous, hydrous silica containing a variable percentage of water, with traces of impurities that are oxides of various metals. Opal is available in two varieties: 1) Precious opal and 2) Common opal. There are many sub-varieties in opal - white opal, black opal, opal matrix, boulder opal, harlequin opal, jelly opal, crystal opal, fire opal, agate opal, wood opal, honey opal etc… Opal is a sensitive to pressure and knocks as well as being affected by acids. Opal is found from Australia, Brazil, Guatemala, Honduras, Indonesia, Japan, Mexico, Russia, Idaho and Nevada.
Onyx:Onyx is a variety of chalcedony that is very porous and is composed of parallel straight layers of different shades of black and white. Many other signal colours are available in onyx. Almost all onyx is artificially coloured. It is translucent or opaque variety.
Peridot:Peridot is also called “Ghrut-mani” in Sanskrit, because of it’s coluor like “Cow-Ghee”. An olivine variety of gem with golden-green, and also shades ranging from dark leek-green to yellowish-green are available in peridot. It has been confused with green corundum or chrysoberyl. Peridot is found from Sri Lanka & Egyptian island of St John’s in the Red Sea.
Pyrite:Pyrite is one of two metallic minerals used as gemstones; the other is hematite. It is pale brassy-yellow and has a brilliant metallic luster. It is the most common and abundant of the several minerals collectively known as “fool’s gold”.
Quartz:Quartz is the name for a group of minerals of the same chemical compassion and similar physical properties. It is one of the most widely distributed mineral in the earth’s crust, sometimes found as elegant crystals whose luster, hardness and watery transparency or conversely, pleasing colours have long been a source of fascination, causing it to be widely employed as a gem or ornamental material. Rock crystal (colourless quartz), amethyst (light to deep purple), smoky quartz (brown to black, smoky gray), citrine (light to dark yellow, golden-brown), prasiolite (leek-green), rose quartz (baby pink), aventurine (green, red-brown, golden-brown), prase (green), blue quartz (turbid-blue), cat’s eye, tiger’s eye, hawk’s eye are the varieties of quartz group.
Rhodochrosite:Rhodochrosite has been on the market only since about 1940. Because of its lovely rose-red colour, it is most desirable ornamental stone. Other main colour is raspberry-red. Its attractiveness is enhanced by its usual variegated nature in which red bands. Deposits of rhodochrosite are found from Mendoza, Mexico, Peru, Chile, United States and South Africa.
Rose Quartz:The name rose quartz is because of its baby pink colour. The colour of this stone often fades in sunlight. Rose quartz is usually turbid, rarely transparent and the colour is presumably due to small amounts of titanium. Rose quartz is pegmatite mineral and is found in large amount at many localities, but deep coloured flawless material is rare. Deposits of rose quartz are found from India, Brazil, Madagascar, Namibia, Mozambique, Sri Lanka, South-West Africa and United States.
Rhodolite:It’s a variety of garnet. Rhodolite is available in deep pink or purplish-red colour and in United States, Tanzania, Zimbabwe and Sri Lanka.
Smoky Quartz:The smoky coloured variety of quartz group. The best known and most productive area is in the Swiss Alps where veins have yielded many tones of beautiful crystals. Other notable localities are in the Brazil, Madagascar, Russia, Switzerland, Ukraine and Scotland.
Spinel:Spinel was recognized as an individual mineral only 160-165 years ago. Before then it was classed as ruby. This gemstone is found in a wide range of colours and shades (colourless spinel being rare), of which the most valuable spinel is that which resembles in colour the red ruby. Spinel comes from Burma (Myanmar), Afghanistan, Sri Lanka & Thailand.
Tanzanite:The blue variety of zoisite discovered in Tanzania in 1967 is commonly known as tanzanite. In good quality the colour is ultramarine to sapphire blue; in artificial light, it appears more amethyst violet. When heated to 750-930 degrees F, the interfering yellowish and brown tints vanish and the blue deepens.
Tiger’s-Eye:A variety of cat’s eye quartz that has originated from crocidolite- a fibrous variety of asbestos, which has partially changed its original greenish-blue colour, by oxidation of the iron pigment, into golden yellow before replacement by quartz. It has a silky luster. Notable localities are India, Australia, Burma, South Africa, Namibia and United States.
Topaz:Formerly, the name topaz was not applied consistently or specifically; one called all yellow & golden-brown and sometimes also green gemstones topaz. The name topaz is most probably derived from an island in the Red Sea, now Zabargad but formally Topazos, the ancient source of peridot. Colours of the gemstone that called topaz are rarely vivid. The most common colour is tallow with a red tint; the most valuable is pink to reddish-orange. Other ranges of colours are pale blue, pale green, pink, golden-brown and sherry-brown. Topaz is very hard but has strong cleavage and breaks easily.
Tourmaline:The name tourmaline is adopted from the Sinhalese word “Turamali” which means mixed coloured stones. Normally this terminology is applied to gems whose identity is disputed. However, the usage of this name has not spread wide. Tourmaline is found in differentiated dikes of silica-rich intrusive rocks and is quite common around granite, where pegmatitic, pneumatolytic mineralizations are abundant. According to colour, many varieties are in trade; like 1) Achroite: colourless or slight coloured variety, quit rare, 2) Dravite: Yellow-brown to dark brown, 3) Indigolite: blue in all shades, 4) Rubelite: pink to red, also with violet tint, ruby colour is most valuable, 5) Schorl: Black coloured & vary common variety. 6) Siderite: lilac to violet blue, 7) Verdelite: green in all shades. Tourmaline is widely distributed,, the black tourmaline is of no value as a gem. The most deposits are in Russia, Sri Lanka, Burma, Brazil, Afghanistan, Zimbabwe, Namibia and Tanzania.
Turquoise (Froza):The name turquoise means “Turkish stone”, because the trade route that brought it to Europe used to come via Turkey. Iron and Copper are the essential components in the chemical composition of turquoise. The iron gives the greenish tone to the gem while the copper imparts the blue body colour. Pure blue colour is rare, mostly turquoise is interspersed with brown, dark gray or black veins of other minerals or the host rocks. The popular sky-blue colour changes at 250 degrees C into a dull green, when soldering be careful for. This material is deposit near the surface by circulating the ground waters that carry copper, aluminum and phosphorous separated from the earlier rocks. Thus turquoise is a secondary mineral. These deposits however are not thick enough to produce thick rocks. It is occasionally found in the alluvial deposits. Being porous it weathers easily on the exposed surfaces. The mines of turquoise are in Iran, Brazil, Australia, Israel, Tanzania, United States, China and Mexico.