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Other Types - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:25:35 +0000

TIGEREYE
Narrow seams of an asbestos mineral replaced by quartz; the original fibrous structure is retained, resulting in chatoyancy in polished specimens; yellow, brownish-yellow, brown, red, blue, green, and streaked in these colors; yellow is by far the most abundant kind; supplied exclusively from South West Africa. Brown and yellow kinds turn red upon heat-treatment; they can also be turned to very pale yellow by bleaching in warm oxalic acid solution. Binghamite is a ligereye from the iron deposits of Minnesota; its fibers are much finer and chatoyancy sometimes greater. (more…)

S - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:24:47 +0000

SMOKY QUARTZ
Includes all varieties with hues from pale brownish smoky to rich brown to nearly black; cairngorm is rich brown material and morion is material of very dark color; can be heat-treated to lighten or drive off color completely; smoky quartz with yellowish tinge is commonly a mixture of smoky and citrine and can be heat-treated to remove the smoky hue and leave behind the pure citrine color; virtually all material is supplied commercially by Brazil but also available from Madagascar, California, Maine, and elsewhere. Favored for faceted gems which are often misleadingly called “smoky topaz.” Also used in carvings, spheres, and other ornamental objects.

R - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:24:24 +0000

ROCK CRYSTAL
Colorless quartz; very abundant in facet-grade crystals to several pounds weight; large flawless pieces capable of cutting spheres in excess of 3″ are rare and cost rises sharply as size increases above this; electronic-grade crystals of 5-10 lbs. may realize as much as f50.00 per pound; much of facet material is left over from the extensive mining for electronic quartz in Brazil during World War II; Brazil continues to be the largest supplier, but good material is available from Arkansas as well as from many other places in the world.
ROSE QUARTZ
Translucent to nearly transparent; from very pale pink to medium rose, some¬times with a bluish tinge; also chatoyant but rarely so pronounced that good star or catseye cabochons can be cut; favored for carvings. Value depends upon intensity of hue coupled with approach to transparency; mainly supplied by Brazil but also from Madagascar, South Dakota, and Canada.
RUTILATED QUARTZ
Recently in abundance from Brazil in fair to superb material containing brilliant coppery to golden rutile fibers in colorless to medium smoky quartz; some fibers occur in broad blades to i/2″ wide, others appear in stellate patterns upon small black tabular hematite crystals; crystals to 10 lbs. weight. Used mainly for specimen pieces but also for cabochons, carvings, and ornamental items.

P - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:24:07 +0000

PRASE
This varietal name was once applied to fine-grained quartzite colored dark green by inclusions of amphibole; some authorities believe it should also apply to green jaspers; the term is now rarely used and material using this name is very seldom sold.

Q - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:23:45 +0000

QUARTZ
The numerous varieties of this mineral provide more inexpensive gem material than all other species combined. Crystalline varieties are those with individual crystals large enough to see with the naked eye or under weak magnification; cryptocrystalline varieties require high magnification and typically con¬tain minute fibrous or granular crystals, commonly arranged in parallel group¬ings forming bands. (more…)

P - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:22:52 +0000

PENTLANDITE
Sometimes cut into cabochons for collectors; brilliant metallic luster.
Ontario lb. 1.00-3.00
PERIDOT, see OLIVINE PERISTERITE, See FELDSPAR PERTHITE, See FELDSPAR PETALITE
Rare pegmatite mineral; colorless to pink; sometimes facetable from clear
areas in colorless crystals from New South Wales; fairly hard, brittle; inclusions
common; collectors’ item only. (more…)

O - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:21:45 +0000

OBSIDIAN
A common glass-like volcanic rock used extensively for tumbled gems, small carvings, ornamental objects, and jewelry; brittle and weak; black most com¬mon but also brown, reddish-brown, and streaked material, the so-called “flow” obsidians; Apache tears are black to dark brown clear nodules weathered from perlite rock; sheen obsidians contain numerous minute spangly inclusions, the best being a gold sheen from Mexico; also rainbow obsidian with colored in¬clusions, sometimes in pronounced bands with or without spangling; also spi-derweb, a brecciated type, and snowflake, a kind with grayish flower-like patches in a black groundmass. Available in large quantities and in large pieces to 10-25 lb. from California, Oregon, Nevada, Mexico. (more…)

N - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:21:17 +0000

NEPHRITE
Fibrous actinolite or tremolite; hard and extremely tough, the classical jade predating jadeite jade and much revered by the ancient Chinese; translucent to nearly opaque; many hues, but seldom as vivid as jadeite, include near-white, tan, yellow, brown, brownish-red, yellow-green, olive-green, dark green to nearly black, etc. Formerly from Khotan, the ancient Chinese source, and from Siberia and Silesia; specimens from these sources are occasionally found in old collections. Currently supplied in large quantities from Alaska, British Columbia, Wyoming, California, and New Zealand. The Chinese prized the off-white Khotan “mutton fat” nephrite, but it is little esteemed in the West; the most valuable nephrites are now the bright greens from Wyoming and New Zealand without traces of olive; as the latter hue appears, the value decreases. “Black” jade from Wyoming is also prized but in reality is a type of very dark olive-green nephrite. The Wyoming fine greens are now very scarce. Unworked material from New Zealand prohibited from export.

M - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:20:51 +0000

MAGNESITE
Rarely in clear facetable crystals from Brazil providing gems to 15 ct. for collectors.
Brazil, colorless, to 50 gm.+ gm. .75-1.50
MAGNETITE
Black magnetic iron ore sometimes cut as a curiosity.
MALACHITE
Bright green copper carbonate known from antiquity and extensively used for ornamental items and carvings, and for beads and other forms of jewelry; soft but dense and fairly tough in thick sections; attractively banded in shades of dark to pale green, the darker material accepting a better polish; often in large masses to many pounds in weight but seldom thicker than 4″ with usual crusts being 1″—2″ thick; slowly alters to a black coating, especially if exces¬sively handled; classic sources in Russia exhausted; sporadic production from Arizona; principally supplied from copper mines in Africa.
(more…)

L - Catalog Of Rough Gemstones

admin — Tue, 04 Dec 2007 01:20:11 +0000

LABRADORITE, See FELDSPAR LAPIS LAZULI
Rock-like gem material in which the blue color is imparted principally by lazurite; also contains calcite as white streaks or spots and pyrite crystals; the finest grade is very fine-grained, uniform in color, lacks calcite, and if it con¬tains pyrite, the latter is in evenly distributed pinpoint crystals; best material from Afghanistan; good mottled material from Lake Baikal region; fair from Chile and abundant; fair to good from California and Colorado but supplies meager. The most compact material can be faceted to a fine finish but most lapis is employed in cabochons, and in small to large carvings.
LAUREUTE, see IDOCRASE LAZULITE
A dark to medium blue mineral resembling lazurite but rare and seldom found in masses large enough to provide cabochons; very rarely, small clear crystals are found in some diamond-bearing gravels of Brazil.
LAZURITE, see LAPIS LAZULI LEPIDOLITE
Soft pink to mauve massive lithium mica rock occurring in pegmatites; has
been used for spheres, bookends, and other ornamental objects; eventually fades.
California, Maine, etc. lb. 1.00-1.25
LEUCITE
Faceting material from ]/$”-l/i” crystals occurring in lavas; very pale straw color; collectors’ gem only.
LIBYAN DESERT GLASS, See TEKTITE LINTONITE, see THOMSONITE LLANITE, LLANOITE
Granite rock containing small blue chatoyant quartz grains in brownish groundmass; soft; useful for ornamental objects only.