IDOCRASE (Vesuvianite)
Relatively abundant in crystals but seldom providing clear areas for faceted gems of over 2 ct.; good cabochon material more common, jade-like material from California being called californite or, sometimes, “California jade.” Fairly hard but mainly cut for collectors.
INDICOLITE, see TOURMALINE
IOLITE (Cordierite)
Unique for strength and character of pleochroism: straw-yellow, blue, dark blue; effect obvious in rough pieces; pieces to 25 gm. common but veil inclusions abundant and clean faceted gems over 5 ct. rare; rarely contains oriented hematite crystals which impart aventurescent effect; more rarely, with silky in¬clusions giving star effect.
IVORY
Includes elephant, narwhal, walrus, and sperm whale (tooth) ivory; attractive brown-stained walrus ivory from Eskimo and Aleut burial sites in Alaska; soft but tough and easily carved.
JADE, See JADEITE Or NEPHRITE JADEITE
Fine-grained massive pyroxene mineral much used for carvings and jewelry gems; classical source Upper Burma; also minor deposits of good material in Japan; fair material from Guatemala and other sources in Mexico or Central America of poor to fair coloration; poor material from California. Burma produces waterworn pebbles and quarry blocks in white, grayish-white, with areas of pale to rich emerald-green, red, brown, yellow, mauve, and black; the emerald-green variety, when intensely hued and translucent, is given the name imperial jade and is very costly; rich greens and rich pure reds are also costly, followed by mauve, yellow, and black; the whitish or grayish-white material, and the faintly greenish varieties which are very abundant in the Burmese de¬posits are cheap; strangely, pure white translucent jadeite is rare and fetches a good price. A very dark green to nearly black jadeite is called chloromelanite; it has little value.
JASPER, See QUARTZ JASPILITE, See QUARTZ JET
Tough black lignite coal, capable of being carved or faceted; defects include splits and soft or porous places; best material from England but supplies
KORNERUPINE
Hard, rare gemstone from gravels of Madagascar, Burma and Ceylon; seldom available: a collectors’ eem.