Semi-valuable Stones

Details

Written by Saonl

ZIRCON

Color: Colorless, yellow, brown, orange, red, violet, biue, green

Color of streak: White Moris’ hardness: 6|~7£ Specific gravity: 3.90-4.71
Cleavage: Imperfect Fracture: Conchoidal. very brittle Crystal system : Tetragonal; short,
four-sided prisms with pyramidal
ends Chemical composition: ZrfSiO^)
zirconium silicate Transparency: Translucent Refractive index: 1.777-1.987 Double refraction : I 0.059 (none in
green stones)
Dispersion: 0.039
Pleochroisrn : Yellow: Very weak; honey, yellow-brown, yellow Red ; Very weak; red, light brown Blue : Definite; blue, yellow, gray, colorless
Absorption spectrum : (Normal) 6910 6890, 6625, 6605, 6535, 6210, 6150, 5895, 5620, 5375, 5160, 4840, 4600, 4327
Fluorescence : Blue : Very weak; light orange Red and brown : Weak; dark yellow
Zircon has been known since antiquity. The derivation of its name is uncertain. Because of its high refractive index and strong dispersion, it has great brilliance and intense fire. It is brittle and therefore sensitive to knocks and pressure. The edges are easily damaged (pack singly ¦ care needed during cutting). Relatively high content of radioactive elements (uranium, thorium) cause large variations of physical properties. Zircons with the highest values in optical properties and specific gravity are scientifically designated as normal or high zircons. Those with lower values are low zircons. The alteration, caused by radioactive elements in green zircons is so advanced that these stones can be nearly amorphous.
Hyacinth: yellow-red to red-brown variety. Starlite: blue variety (heat-treated).
Deposits are mostly alluvial and arc found in Cambodia, Burma, Thailand and Sri Lanka; also in Australia, Malagasy Republic, Tanzania, Vietnam and France (Haute Loire).
In nature the gray-brown and red-brown zircons are the most common. Colorless specimens are rare. In the South Asiatic countries where found, the brown varieties are heat-treated at temperatures of 1472-1832°F/8OO-IOOO”C, producing colorless and blue zircons. These colors do not necessarily remain constant, ultra-violet rays or sunlight can produce changes. Colorless stones are brilliant cut; colored ones are given a brilliant or emerald cut. Synthetic zircons are scientifically of great interest. Green zircons are rare in the trade, and are in demand by collectors.
Can be confused with aquamarine, cassiterite, chrysoberyl, hessonite, sapphire, sinhalite, synthetic spinel, sphene, topaz, tourmaline and idocrase. Colorless heat-treated zircon has been fraudulently offered for diamond (p. 70) as “matara diamond”. All zircons (except the green) have strong double refraction, which can readily be seen under the loupe at the facet edges, an important identification mark.

TOURMALINE
Color: Colorless, pink, red, yellow, brown, green, blue, violet, black, mutti-colored

Color of streak : White
Mohs’ hardness: 7-7^
Specific gravity: 3.02-3.26
Cleavage: None
Fracture: Uneven, small conchoidat, brittle
Crystal system : Hexagonal (trigonal); usually long crystals with triangular cross section and rounded sides, definite striation parallel to main axis, often several prisms grown together
Chemical composition : (NaLiCa) . (FeuMg Win AI)8AI8(<0H)4 fB03)3Si60,8) aluminium boraie sliicate, complicated and changeable composition
Transparency: Transparent, opaque Refractive index : 1.616-1.652 Double refraction: —0.014 to —0,044 Dispersion: 0.017 Pleochroism : Red : Dark red-light red
Yellow: Definite; dark yellow-light
yellow
Brown : Definite; dark brown-light
brown
Green : Strong ; dark green-light
green
Blue : Strong; dark blue-light blue Absorption spectrum: Red: 5550,
5370, 5250-4610, 4560, 4510, 4280
Green: 4970,4610, 4150 Fluorescence: Colorless: Weak;
green-blue
Pale yellow: Weak; green-blue
Red: Weak; red-violet
Pink, brown, green, blue ; none
No gemstone has such richness in color variation as tourmaline. Known in antiquity in the Mediterranean area, the Dutch imported it in 1703 from Sri Lanka into Europe. They gave the new stone a Sinhalese name Turamali, the original meaning of which is not known.
According to color, the following varieties are recognized: Achroife (Greek - without color) colorless or nearly so. Rare. Rubellite (p. 113 nos. 2, 4) (Latin - reddish) pink to red, sometimes with a violet tint; ruby color most valuable.
Dravite yellow brown to dark brown.
Verdclite (Italian/Greek - greenstone) green in all shades,-most common of all tourmalines. Emerald green most valuable. Indigollte or Indicolite blue in all shades. Siberitc (after finds in Urals) lilac to violet blue. Sometimes used as synonym for rubellite.
Schorl black, very common. Rarely used for jewelry. Name derived from old mining term.
Uni-colored tourmalines are quite rare. Most crystals have various color shades or even different colors (6, 8). Often there is some layered color. Brazil produces stones with a red interior, inner “skin” white, outer “’skin” green. The South African tourmalines are green inside and the outer layer is red. A tourmaline with a red inside and a green “skin” is sometimes called a “watermelon”. The nuances and colors are particularly effectively shown when slices of cross-section are polished.

ROCK CRYSTAL
Quartz group

Color: Colorless Color of streak: White Moris’ hardness; 7 Specific gravity: 2.65 Cleavage: None
Fracture: Conchoidal, very brittfe Crystal system : Hexagonal (trigonal); hexagonal prisms
Transparency: Transparent Refractive index: 1.544-1.553 Double refraction: -|-0.GQ9 Dispersion; 0.013 Pleochroism: None Absorption spectrum: Not usable Fluorescence: None
The name crystal comes from the Greek for “ice”, as it was believed that rock crystal was eternally frozen. Rock crystals weighing many tons have been found. Cuttable material is rare. Inclusions are of goethite (star quartz, no. 12), gold, pyrite, rutile and tourmaline (p. Ill no. 5). They are found all over the world and are mainly used as costume jewelry and to imitate diamonds. Can be confused with all colorless gems and glass. It becomes smoky when treated with radium and x-ray. Synthesized for industrial purposes only. Rhinestones, formerly rock crystal pebbles from the Rhine, are today multi¬colored glass imitations.

SMOKY QUARTZ
Quartz group, falsely called smoky topaz

Color: Brown to black, smoky gray Color of streak: White Viohs’ hardness: 7 Specific gravity: 2.65
Cleavage: None
Facture: Conchoidal, very brittle
Crystal system : Hexagonal (trigonal); hexagonal prisms
Transparency: Transparent Refractive index; 1.544-1.553
Double refraction : -f 0.009 Dispersion: 0.013
Pleochroism: Dark: Definite; brown, reddish brown
Absorption spectrum : Not usable Fluorescence: Usually non.
Jamed after its smoky color. Very dark stones are called “morion”. Pales /hen heated to 572-752°F/300-400°C; there are frequent inclusions of rutile eedles (1, 2). Found worldwide; Scottish variety is called “cairngorm”-’an be confused with andalusite, axinite, sanidine, tourmaline and idocrase.
Smoky quartz with rutile inclusions Smoky quart? with rutile, cabochon Smoky quartz, oval, 3.8g Smoky quartz, two crystals Smoky quartz, octagon, 5.6g Smoky quartz, oval, 6.2g Smoky quartz crystal.

QUARTZ
Minerals of the same or similar chemical composition are included under the single group of Quartz (SiOs resp. SiOa.nHaO) silicon dioxide: Macrocrystaliinc quartz includes amethyst, aventurine, rock crystal, citrine prase, hawk’s eye, quartz cat’s eye, smoky quartz, rose quartz and tiger’s eye.’ Microcrystailine quartz includes chalcedony group - agate, fossilized wood chrysoprase, heliotrope, jasper, cornelian, moss agate, onyx, sard. Amorphous quartz includes opal group-precious opal, fire opal, common opal.

ROCK QUARTZ CAT’S EYE (1, 2) quartz group
Color: White, gray, green, yellow, Chemical composition : SiO2 silicon

brown dioxide
Color of streak: White Transparency: Translucent, opaque
Mohs’ hardness: 7 Refractive index: 1.544-1.553
Specific gravity: 2.65 Double refraction: 4-0.009
Cleavage: None Dispersion: 0.013
Fracture: Irregular Pfeochraism: None
Crystal system: Hexagona (trigonal) Absorption spectrum : Not usable
fibrous aggregate Fluorescence: None
Compact quartz with fibrous, parallel hornblende. Not to be called “cat’s eye” without the prefix of quartz, as that term refers to chrysoberyl cat’s eye (cymophane p. 98). Sensitive to acids. Found in Sri Lanka, also in India and Brazil. Cut en cabochon, shows chatoyancy like a cat’s eye. Can be confused with chrysoberyl cat’s eye (p. 98). Sometimes de-colored hawk’s eyes or tiger’s eyes are substituted.
HAWK’S EYE (3, 4) quartz group, also called Falcon’s Eye
Finely fibrous quartz aggregate with crocidolite (type of hornblende), blue-gray to blue-green. Iridescence of planes; fractures have silky luster. It is sensitive to acids. Found in South Africa together with tiger’s eye. Used for ornamental objects, rings, pendants. Cabochons show chatoyancy (small ray of light on surface) which is reminiscent of the eye of a bird of prey.
TIGER’S EYE (5. 6) quartz group

Color: Gold-yellow, gold-browrt Transparency: Opaque
Color of streak; Yellow-brown Refractive index : 1.544-1.553
Mohs’ hardness: 7 Double refraction: 4-0.009
Specific gravity: 2.64-2.71 Dispersion: 0.013
Cleavage: None PJeochroism: None
Fracture: Fibrous Absorption spectrum : Not usable
Crystal system : Hexagonal (trigonal); Fiuorescence: None
fibrous aggregate
Chemical composition : SiO2 silicon
dioxide
Formed from hawk’s eye through pseudomorphism of crocidolite in quartz, keeping the fibrous structure. Brown iron produces the golden-yellow color. There is chatoyancy on the fractures and a silky luster. It is sensitive to acids. Found together with hawk’s eye in slabs of a few inches thickness, the fibers being perpendicular to the slab. The most important deposit is in South Africa; also found in Western Australia, Burma, India and the U.S. (California). Used for pendants and objets d’art. When cut en cabochon, the surface shows chatoyancy reminiscent of the eyes of a cat.

TANZANITE
Cofor: Sapphire blue, amethyst, violet

Transparency; Transparent
Color of streak: White
Refractive iiidex: 1.691-1,700
Mohs’ hardness: 6f-7
Double refraction: +0.009
Specific gravity: 3.35
Dispersion: 0.030
Cleavage: Perfect
Pleochroism : Very strong; violet blue,
Fracture: Uneven, brittle brown
Crystal system: Orthorhombic, multi
Absorption spectrum : 7100, 6910, faced prisms, mostly striated 5950, 5280, 4550
Chemical composition: Ca2AIB
Fluorescence: None
(0/OH/SiO4/SiaO,) calcium aluminium silicate
The name tanzanite (after the East African state of Tanzania) was introduced by the New York jewellers Tiffany & Co. It is accepted by the trade, although scientists do not encourage a multitude of names for gemstones and refer to it as blue zoisite. In good quality the color is ultramarine to sapphire blue; in artificial light, more amethyst violet. When heated to 752-932°F/400-500°C, the yellow and brown tints vanish, and the blue deepens. Tanzanite cat’s eyes are also found. Some deposits in Tanzania near Arusha occur in veins or filling of fissures of gneisses.
There are glass imitations on the market; also doublets of glass with a tanzanite crown, or of two colorless synthetic spinels glued together with tanzanite-colored glue. Can be confused with sapphire and synthetic blue-violet corundum.

PERIDOT
also called olivine, chrysolite

Corot: Yellow-green, olive green.
Transparency: Transparent brownish
Refractive index: 1.654-1.690
Color of streak: White
Double refraction : +0.036
Mohs’ hardness: 6^-7
Dispersion: 0.020
Specific gravity: 3.27-3.37
Pfeochroism : Very weak; colorless to
Cleavage: Imperfect pale green, lively green, olive green
Fracture : Brittle, small conchoidal
Absorption spectrum: (6530), (5530),
Crystaf system : Orthorhombic; short, 5290, 4970, 4950, 4930, 4730, 4530
compact prisms, vertically striated
Fluorescence: None
Chemical composition: (Mg, Fe)2
SiOj magnesium iron silicate
The name derives from the Greek, but the meaning is uncertain. Perhaps it refers to the numerous crystal planes of the crystal. The name “chrysolite” (Greek - gold stone) was formerly applied not only to peridot but also to many similarly colored stones. The name commonly used in mineralogy is olivine (because of its olive green color).
It has a vitreous and greasy luster, and is not resistant to sulphuric acid. It tends to burst under great stress, therefore is sometimes metal-foiled. Dark stones can be lightened by burning. Rarities are peridot cat’s eye and star peridot.
The most important deposits are in the Red Sea on the volcanic island of St. John, 388 miles/300 km east of Asswan; they have been mined for 3500 years. Beautiful crystals can be found on the walls of cavities of weathering peridot rock. Good material can also be obtained from serpentine. There are also quarries in upper Burma (19 miles/30km northeast of Mogok). Less important finds have been in Australia (Queensland), Brazil (Mirias Gerais), South Africa (together with diamond), the U.S. (Arizona, Hawaii, New Mexico) and Zaire. In Europe peridot is found in Norway, north of the Nord Fjord.
Peridot was brought to Europe by the crusaders in the Middle Ages and was often used for ecclesiastical purposes. It was very popular during the baroque period. It is not greatly desired by the trade because of its lower hardness. Used in table and emerald cuts, sometimes as brilliant. Usually set in gold.
The largest cut peridot weighs 310ct and was found on the island of St. John. It is at present in the Smithsonian Institution in Washington, D.C. In Russia there are some cut peridots which came out of a meteorite which fell in 1749 in east Siberia.
Can be confused with beryl, chrysoberyl, dsmantoid, diopside, moldavite, prasiolite, prehnite, sinhalite, emerald, synthetic spinel, tourmaline and idocrase. The strong double refraction is an important distin¬guishing mark. In thick stones the doubling of the edges can be seen with the naked eye.

CHALCEDONY
Quartz group

Chalcedony describes a group of micro-crystalline quartzes: agate, dendritic agate, chalcedony, chrysoprase, heliotrope, fossilized wood, jasper, cornelian, moss agate, onyx and sard, as well as a bluish variety of chalcedony. Some scientists describe chalcedony as the fibrous variety and classify the grainy jasper in a separate group. The nomenclature in the trade is even more’ confusing. The name chalcedony is derived from an ancient town on the Bosphorus. While the crystal quartzes (rock crystal, amethyst) have a vitreous luster, chalcedonies are waxy or dull.
CHALCEDONY (4-6) quartz group
Color: Bluish, white, gray Transparency: DulS,translucent
Color of streak: White Refractive index: 1.630-1.539
Mohs’ hardness: 6^7 Double refraction ; up to +0.006
Specific gravity: 2.58-2,64 Dispersion: None
Cleavage: None Pleochroism: None
Fracture: Uneven, shell-like Absorption spectrum: Dyed blue:
Ctystal system: Hexagonal (trigonal); 6900-6600,6270
fibrous aggregates
Fluorescence: Blue-white
Chemical comp.: SiO2 silicon dioxide
While the microscopic fibers are parallel and perpendicular to the surface, chalcedony shows macroscopically radiating stalactitic, grape-like or kidney shapes (4). Always porous; can therefore be dyed. Natural chalcedony has no layering or banding. The trade also offers parallel layered, artificial blue-colored agate as chalcedony (5). There is a wide distribution of deposits, especially in Brazil, India, the Malagasy Republic and Uruguay. In ancient times used for cameos and as a talisman against idiocy and depression. Today used for ornamental objects, in gem engraving and as cabochons.

CORNELIAN
Quartz group

The name is derived from the Cornel type of cherry because of its color. It is the flesh-red to brown-red variety of chalcedWy. The best qualities come from India, where the brown tints are enhanced to red by exposure to the sun. Most cornelians arc agates from Brazil and Uruguay, colored with ferrous nitrate solution. When held against the light, the colored variety shows stripes, the natural variety has a cloudy distribution of color. In antiquity it was thought to still the blood and soften anger. Use and additional data as with chalcedony.

AGATE
Quartz group

Color: Various, banded or layered
Transparency: Translucent, opaque
Color of streak: White Refractive index: 1.544-1.553
Mohs’ hardness: 6^-7
Double refraction :0.009
Specific gravity; 2.60-2.65
Dispersion: None
Cleavage: None Pleochroism : None
Fracture: Uneven
Absorption spectrum : Dyed yellow:
Crystal system : Hexagonal (trigonal); 7000, (6650), (6340)microcrystalline aggregates
Fluorescence : Varies with bands:
Chemical composition : SiO, silicon partly strong, yellow, blue-white dioxide.
The name agate is derived from the Sicilian river Achates where agates were probably found in antiquity. It is not certain whether or not this is the river Dirillo in the south-east of the island.
Agate is a banded chalcedony, sometimes containing opal substance. The individual bands can be multi-colored, or more or less of the same color. The agates of the exhausted German mines were red, pink and brown, separated by gray bands. The South American agates are usually dull gray without special markings; therefore they are usually treated (p. 136). Transparency varies from nearly transparent to opaque.
Agates are found as nodules or geodes in siliceous volcanic rocks (mela-phyre, porphyry) with sizes varying from a fraction of an inch to a circum¬ference of several yards. The bands are formed by rhythmic crystallization, but scientific opinions vary as to how. It was thought that the agate bands crystallize gradually in the hollows formed by gas bubbles from a siliceous solution. Now the theory that their formation is simultaneous with that of the matrix rock, has won support. According to this idea, the liquid drops of the silicic acid cool with the cooling rock and produce a layered crystallization from the outside. The various bands - especially those close to the outer wall - may vary in thickness, but normally their thicknesses remain constant throughout the nodule. The outer wall and the outermost layer may form a white crust due to weathering.
Where the inner cavity of the nodule is not filled with an agate mass, well-developed crystals can form in the remaining spaces: rock crystal , amethyst or smoky quartz, sometimes accompanied by calcite, hematite, chalybite and zcol ite. A nodule with crystals in the central cavity is called a geode .
Varieties: According to sample, design or structure of the agate layer, trade and science have given various names to the agates. Eye agate: ring shaped design with point in center. Layer agate: layers parallel to skin .
Dendritic agate: colorless or gray-white translucent chalcedony with dendriles (p. 131 nos. 1-4). Not layered, not real agate,
Enhydritic agate: agate or chalcedony nodule, partly filled with water which can be seen through the walls. After the agate is taken from surrounding rock, the water often dries out.
Fortification agate: patterned like the ground-plan of an old-fashioned fortress.
Orbicular agate: circular layer
group: eye agate.
Moss agate: colorless, translucent chalcedony with moss-like inclusions of hornblende. Is not layered and not really agate.
Scenic agate: shows scenery-like image by brown or reddish coloring and included dendrites.
Pseudo-agate: interior similar to agate with layering and geode opening, although outside not nodule-like, but geometric shape. As they are not symmetrical, these forms are not crystals and not derived from such. It is not known how these were formed. Found in Brazil. Length of individual piece can measure up to 28in/75cm. Deposits discovered only recently. Also called polyhedric quartz.
Tubular agate: full of feeding canals. Sard stone: agate with parallel layers. Brecciated agate: broken agate pieces held together with quartz.
Deposits: The most important agate deposits at the beginning of the 19th century were in the neighborhood of Idar-Oberstein, Germany. Today these have been worked out. Rarely larger than the human head, they have beautiful colors such as gray, red, pink, yellow, brown and pale blue. These could not be dyed.

Nephrite
(Greek - kidney) is even tougher than jade. Occurs in all colors, also striped and spotted. The most valuable color is green.

Nephrite is more common than jadeite. It is found in the west of Sinkiang (China), near Kashgar and Khutan in serpentinite and in river pebbles. On the west end of Baikal Lake, there is a spinach green variety (Russian jade). The large deposits on the south island of New Zealand are not very important on the world market, because exports of raw material have been prohibited. Further deposits are in Australia (Tasmania), Burma, Brazil, Canada (British Columbia), Mexico, New Guinea, Taiwan and in Poland.
Jadeite and nephrite are used for jewelry in ornamental and religious objects, It used to be cut with quartz sand; today carborundum or diamond powder is used, The main cutting centers are Canton, Peking and Hong Kong, There are many imitations on the market; also triplets of jade topped with a dull jade cabochon on top of which translucent jade is fixed. Green glue helps it to appear like imperial jade. It is also dyed to improve the color. For magnetite-jade, see p. 206. Can be confused with agalmatolite, amazonite, aventurine (p, 122), bowenite, californite, chrysoprase, Connemara marble, grossular, plasma, prase, prehnite, serpentine, smithsonite, verd-antique) and williamsite.
Color: Green, also white, gray.
Chem. comp: Ca2(Mg,Fe)5 (Si4On)2
yellowish, reddish, brown, often (OH)2 calcium mag. iron silicate
spotted Transparency:Opaque
Color of streak: White
Refractive index: 1.600-1.627
Mohs’ hardness: 6-6^
Double refraction: —0.027, often none
Specific gravity: 2.90-3.02
Dispersion: None
Cleavage: Lengthwise, perfect
Pleochroism ; Weak; yellow to brown,
Fracture: Splintery, sharp edged, green
brittle Absorption spectrum: (6890), 5090,
Crystal system: Monoclinic,
Fluorescence: None

HEMATITE
or bloodstone, speculate

Color: Black, black-gray, brown-red
Transparency: Opaque
Color of streak: Blood-red
Refractive index : 2.94-3.22
Mohs’ hardness: 5{-6£
Double refraction : —0,28
Specific gravity: 4.95-5.16
Dispersion : None
Cleavage: None
Pleochroism ; None
Fracture : Conchoidal, uneven, fibrous
Absorption spectrum: (7000), (6400),
Crystal system: Hexagonal (trigonal) platycrystals
Chemica composition : Fe2O3 iron
Fluorescence: None oxide
The name (Greek - blood) derives from the fact that, when cut, the coolant is colored red. Shiny hematite crystals are sometimes called specularite (Latin -mirror) as they were used as a mirror in ancient times.
When cut into thin plates, hematite is red and transparent; when polished, it is very shiny. Cuttable material comes from Cumberland (England), Saalfeld (Germany) and the island of Elba, as well as from Norway, Sweden, Spain, Brazil, New Zealand and the U.S. In antiquity, it was used as an amulet against bleeding. Formerly used as mourning jewelry, but today is mainly used for ring stones, bead-necklaces and intaglios (engravings). Can be confused with cassiterite. Has been imitated by pressing and sintering hematite splinters.

OPAL
Quartz group

The name is derived from an Indian word for “stone”. It is divided into three groups: the opalescent precious opals, the yellow-red fire opals and the common opals. Their physical properties vary considerably.
Color: White, gray, biue, green,
Transparency: Transparent, opaque orange
Refractive index : 1.44-1.46
Color of streak: White
Double refraction: None
Mohs’ hardness: 55-6^
Dispersion: None
Specific gravity: 1.98-2.20
Pleochroism: None
Cleavage; None
Absorption spectrum: Fire opal:
Fracture: Conchoiclal, splintery, brittle 7000-6400, 5900-4000
Crystal system : Amorphous; kidney
Fluorescence: White: white, bluish,
or grape-shaped aggregates brownish, greenish
Chemical composition: SiO2.nHaO Black: usually none hydrous silicon dioxide
Fire: greenish to brown
PRECIOUS OPAL
The special characteristic of these gems is their opalescence, a rainbow-like iridescence which changes with the angle of observation. Until the 1960s, this was thought to be caused by the refraction of light from the thin surface layers. The real cause was discovered under the electron microscope using a magnification of 20,000: tiny spheres (0.00i of a millimeter in diameter) of the mineral Cristobal ite layered in siliceous jelly cause the reflection or interference appearances. Strictly speaking, precious opal is not really amorphous.
Opal always contains water; the content varies but it can be as much as 30%. It can happen that in the course of the time, the stone loses water, cracks and the opalescence diminishes. This can, at least temporarily, be restored by saturation with oil or water. The aging process is avoided and the opalescence increased when stored in moist absorbent cotton (cotton wool). Care must be taken during setting. A little heat can evaporate the water. Opal is also sensitive to pressure and knocks as well as being affected by acids and alkalies.
Two groups of precious opals can be distinguished: those with a white or light basic color, known as white or milky opals, and the rarer black opals . Their basic color is dark gray, dark blue, dark green or gray black. Deep black is rare.
Opal matrix (formerly known as opaline) is a banded or leafed inclusion of precious opal in the matrix rock. Cut as gemstones because of the contrast with associated materials .
Precious Opal
Up to the turn of the century, the andesite lavas of Czechoslovakia supplied the best qualities. Then the Australian deposits were discovered. Famous deposits in New South Wales are at Lightning Ridge and White Cliffs; in South Australia at Coober Pedy and Andamooka; in Queensland at Bulla Creek and Burcoo River. Most of the 0.04-0.08in/l-2mm thin opal layers are bedded in sandstone. Further deposits are found in Brazil, Guatemala, Honduras, Japan and the U.S. (Nevada).
In Europe precious opal has been thought of as unlucky, but in the Orient it stands for loyalty and hope, The play of color is seen best if it is cut en cabochon. Very thin pieces of opal are sometimes mounted on a piece of common opal or onyx; this is the opal doublet. Triplets are also made with a protective top layer of rock crystal.
Fakes are prepared by coloring black or matrix opal in order to liven up the play of color; they are also made by impregnating porous opal with artificial resin, In 1970 white and black opal was synthesized in France.
FIRE OPAL
Named after its orange color. It does not opalesce and is usually milky and turbid. The best qualities are clear and transparent, They are very sensitive to every stress. Important deposits are in Mexico (Hidalgo and Queretaro Provinces), also in Brazil, Guatemala, Honduras, U.S., Western Australia and Turkey (Simavopal). Glass imitations are found on the market.
Girasol: (”Sunflower”) nearly colorless, transparent variety with slight bluish sheen and red play of color. A name sometimes given to girasol or fire opal is sun opal,
Mexican Water Opal: variety from Mexico, colorless or slightly brown, transparent with unicolored schiller.
COMMON OPAL
Mostly opaque, without play of color, it is quite common. Many names are used for it in trade such as: agate opal, hyalite (colorless, transparent), wood opal (agatized wood), honey opal, milk opal (translucent, whitish, pearly luster; an opaque variety is called porcelain opal, if dendrites are included moss opal, no. II), rnother-of-pearl opal or cacholong (opaque to translucent, white or yellowish with mother-of-pearl luster), prase opal formerly called chrysopal, wax opal, and hydrophane (precious opal, turbid by loss of water, can temporarily become transparent and opalescent by absorption of water).

LAPIS LAZULI
Called lapis for short, sometimes lazurite

Transparency: Opaque Refractive index: About 1.50 Double refraction: None Dispersion: None Pleochroism : None Absorption spectrum : Not usable Fluorescence: Strong; white
Color; Blue
Color of streak: Light blue
Moris’ hardness: 5-6
Specific gravity: 2.4-2.9
Cleavage: None
Fracture: Conchoidal, grainy
Crystal system : Isometric; crystals
rare, mostly dense, grainy aggregate Chemical composition : Na8
(AiBSi60a4)S2 sulphur containing
sodium aluminium silicate
As lapis lazuli (arabic-latin - blue stone) is composed of several minerals - if only in small quantities (augite, calcite, diopside, mica, haiiynitc, hornblende, pyrite) - some experts consider it not to be a mineral, but a rock; the main ingredient being lazurite.
It is very sensitive to pressure and high temperatures, hot baths, acids, and alkalies. It has a vitreous to greasy luster. In the best quality the color is regularly distributed, but it is usually spotted or striped. In Chilean and Russian stones, the protruding white calcite diminishes the value. Well distributed fine pyrite is advantageous and is taken to show genuineness. Too much pyrite causes a dull, greenish tint.
Mineable deposits are rare. For centuries the most important deposit with the best qualities has been in the West Hindu Kush mountains of Afghanistan near the source of the river Amu-Darja. Lapis lazuli is mined under primitive conditions and in difficult terrain where it is present as an irregular occurrence in limestone. The Russian deposits are at the south west end of Baikal Lake. The matrix rock is white dolomitic marble. Chile supplies lower quality stones with many white spots of calcite. The deposits are north of Santiago in the Coquimbo Province.
Lapis was used for jewelry in antiquity. During the Middle Ages, it was also used as a pigment to produce aquamarine. Some castles have wallpanels and columns covered in lapis. Today it is used for ring stones and necklaces, Chilean lapis is used for carvings and ornamental objects.
The finely-grained, gray-brown jasper from Nunkirchen is colored with prussian blue and sold as an imitation under the name of “Swiss lapis.” In 1954 a synthetic grainy spinel, colored with cobalt oxide, with a good lapis color made an appearance on the market. Inclusions of thin gold pieces simulated the pyrite and improved the character of the genuine stone.
Can be confused with azurite, dumortierite, lazulite, sodalite and glass imitations.

FLUORITE
Also called fluorspar

Color: Colorless, red, orange, yellow, green, blue, violet, nearly black
Color of streak: White
Mohs’ hardness: 4
Specific gravity: 3.T8
Cleavage: Perfect
Fracture: Even to conchoidal, brittle
Crystal system : Isometric; cubes, octahedra
Chem. comp: CaF2 calcium fluoride
Transparency: Transparent, translucent
Refractive index : 1.434
Double refraction: None
Dispersion: 0.007
Pleochroism: None
Absorption spectrum: Green; 6400,6006, 5850, 5700, 5530, 5500,4520, 4350
Yellow: 5450, 5150, 4900, 4700, 4520
Fluorescence: Usually strong; blue-violet
Has a zonal or spotty distribution of color, which can be changed by radiation, also a vitreous luster. There are deposits in West Germany (Wolsendorf/ Oberpfalz) and England (Cumberland, Derbyshire, where the blue-layered I “Blue John” is found). Can be synthesized; confused with many gemstones.

APATITE

Color: Colorless, pink, yellow, green.

Color of streak : White to yellow-gray
Dispersion: 0-016
Mohs’ hardness: 5 Pleochroism : Green : weak; yeifow,
Specific gravity: 3.17-3.23 green
Cleavage: Poor Blue: very strong; blue, colorless
Fracture: Conchoids!, brittle
Absorption spectrum : Yellow-green:
Crystal system : Hexagonal, short and 6053, 6025, 5975, 5855, 5772,5742 long columns, thick tabular with 5335, 5295, 5270, 5250, 5210, 5140, numerous faces 4690,4425
Chem.comp: Ca3(F,CI,OH)(PO4)3 Blue: 6310, 6220, 5250, 5120, calcium fluoro- and chioro- 5070,4910, 4640 phosphate
Fluorescence: Very variable
Transparency: Transparent
Has a vitreous luster and is sensitive to acids. It is found in upper Burma, Brazil, Sri Lanka, Czechoslovakia, India, Malagasy Republic, Mexico and the U.S. Green variety called asparagus-stone. Apatite cat’s eye is found in Burma and Brazil. Confused with beryl, topaz, tourmaline.

SPHEIME
Also called titanite

SPHEIME (7, 8) also called titanite
Color: Yellow, brown, green
Color of streak: White
Mohs’ hardness: 5-5^
Specific gravity: 3.52-3.54
Cleavage: Perfect
Fracture: Conchoidal, brittle
Crystal system : Monoclinic; wedge-shaped crystals
Chemical composition: CaTis(0/SIO4) calcium titanium silicate
Transparency: Transparent Refractive index: 1.885-2.050 Double refraction: +G.105 to +0.135 Dispersion : 0.051 Pleochroism : Green : colorless, green
Yellow : strong; colorless, yellow,
reddish Absorption spectrum : 5900, 5860,
5820, 5800, 5750, 5340, 5300, 5280 Fluorescence; None
Very intense fire, it has an adamantine luster as well. Found in Mexico and Brazil. Can be corifused with many gems.

RHODOCHROSITE

Color: Rose-red to white, striped manganese carbonate
Color of streak: White
Transparency: Opaque to transparent
Moris’ hardness: 4

Refractive index; 1.600-1.820

Specific gravity: 3.30-3.70
Double refraction:—0.22
Cleavage: Perfect
Dispersion: None
Fracture: Uneven, conchoidal
Pleochroism: None
Crystal system : Hexagonal (trigonal).
Absorption spectrum : 5510, 4545,
rare, rhombohedra usually compact, 4100, 3910, 3830, 3780, 3630
longish aggregates Fluorescence: Weak; red
Chemical composition: MnCOa

The name refers to the color (Greek - rose red). It has, on occasion, been called inca-rose because of the location of the main deposits. The aggregates are light-dark striped with the layers very notched. It has a vitreous luster; on cleavage faces, there is a pearly luster. Raspberry red is the most common color. The most important deposit is in Argentina, near San Luis, 144 miles/ 230km east of Mendoza. The rhodochrosite has formed as stalagmites in the silver mines of the Tncas since they were abandoned in the 13th century. Further deposits arc in Argentina and in the U.S. (Colorado).
Usually used in larger pieces, as then the marking is more distinct, for ornamental objects as well as for cabochons and bead necklaces. Can be confused with rhodonite (see below).

MALACHITE
Color: Light green, emerald green,black-green

Cofor of streak : Light green Mohs’ hardness: 3^-4 Specific gravity: 3.75-3.95 Cleavage: Perfect Fracture: Splintery, scaly Crystal system: MonocSinic; small,
long prismatic crystals, aggregates
with fine needles
Chemical composition: Cu2
(OHJiCOa) basic copper carbonate Transparency: Opaque Refractive index : 1.655-1.909 Doubie refraction: —0.254 Dispersion: None Pleochroism : Very strong; colorless,
green
Absorption spectrum : Not usable Fluorescence: None
The name could be derived from its color (Greek malache= mallow), perhaps from its low hardness (Greek malakos, soft). When cut, it shows layers of lighter and darker concentric rings, parallel lines or other shapes caused by its shell-like formation. Large uni-colored pieces are rare. Sometimes inter-grown with azurite which produces Azur-malachite (p. 175, no. 8 and p. 29) and with turquoise and chrysocolla to produce Eilat stone (p. 201, no. 8).
The malachite aggregates are formed from very small crystals. Larger crystals arc very rare and in demand by collectors, There is a weak vitreous luster in rough pieces on fresh fractures; when polished the luster is silky. It is sensitive to heat and acids, ammonia and hot waters. Occurs in rounded nodules, grape shapes, stalactitic and, rarely, in encrusted slabs. Formed from copper-containing solutions in or near copper ore deposits. The most impor¬tant deposit used to be in the Urals near Swerdlowsk (formerly Jekaterinen-burg). From there the Russian Tsars obtained the malachite for decorating their castles, panelling the walls, and for beautiful inlaid works.
Today Zaire is the most important malachite producer as far as quality and quantity is concerned. Some of the stones are cut near the mine, some reach the world market as raw material. Further deposits are in Australia, Chile, Rhodesia (lighter quality), South Africa and the U.S. (Arizona).
Malachite was popular with the ancient Egyptians, Greeks and Romans for jewelry, amulets and as a powder for eye shadow. During the Middle Ages, it was thought to cure vomiting and to protect against witches and other dangers to small children. It is used as pigment for mountain green.
Although it is not very hard and not very resistant, malachite is popular for jewelry and ornaments. Used en cabochon and in slightly rounded table stones for necklaces and especially for objets d’art, such as plates, boxes, ashtrays and figures. The cutter must work the malachite so as to show the decorative marking to its best advantage. Concentric eye-like rings are most popular.
Not easily confused with other stones in larger pieces because of the striped character, but small unstriped stones can easily be confused with any opaque green stones.