Idocrase is one of the lesser known and more beautiful collector gems. When properly cut it is as bright and attractive as the grossular garnets, which it so strongly resembles. The complexities of its chemistry lead to a huge range in properties and colors. Cuttable material is known from Italy (brown and green), Quebec (pale green, bright yellow), New York (brown), Pakistan (green), Kenya (brown and green).
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|Alternate Common Names||Vesuvianite|
|Crystallography||Tetragonal. Crystals often well formed, prismatic, pyramidal, often with complex modifications; granular, massive. Often intergrown with grossular.|
|Colors||Colorless, green (various shades), brown (various shades), white, yellow (various shades), red, brownish red, blue, blue-green, pink, violet. Sometimes color zoned.|
|Luster||Vitreous to resinous.|
|Hardness||6-7. Note: Antimonian idocrase from contact metamorphic rocks, greenish-yellow grains, e= 1.758-1.775, o = 1.775-1.795; birefringence 0.017-0.025; Sb2O3 >15%.|
|Cleavage||None. Fracture conchoidal.|
|Stone Sizes||Crystals up to several inches in length occur at a few localities, but these are seldom transparent except in small areas. The maximum expectable size for a faceted idocrase is on the order of 10 carats (for brown material from Italy and Africa), perhaps 15 carats in green material. Smithsonian Institution (Washington, D.C): 3.5 (brown, Italy); 7.1 (brown, Tanzania). Devonian Group (Calgary, Alberta, Canada): 8.50 (brown, Africa). National Museums of Canada (Ottawa, Ontario): 3.15, 2.95, 2.28 (Laurel, Quebec).|
|Spectral||Strong line at 4610, weak at 5285.|
|Formula||Ca19Al4Fe(Al,Mg,Fe)8Si18 O7(O,OH,F)8 + Be, Cu, Cr, Mn, Na, K, Ti, B. H20, U. Th, Zn, Sn, Sb, rare earths.|
|Pleochroism||Usually weak in same colors as crystal. Also green/orange and green/yellow-green (from Quebec).|
Optics: Variable depending on paragenesis and mineral associations.
Uniaxial (+) or ( – ); sometimes anomalously biaxial (-) or (+); twinned.
Incredible array of elements substitute in the idocrase structure.
Occurrence: Serpentines and related rocks; contact metamorphic deposits, especially in limestones and dolomites: alkalic rocks; regionally metamorphosed rocks.
Finland, Japan; Korea; Tanzania.
California: californite; also crystals at Pulga.
Ala, Piedmont, Italy: fine brown and green crystals.
Zillerthal, Tyrol, Switzerland: brown crystals; also at Zermatt, other locations.
Laurel, Quebec, Canada: bright yellow grains and masses. Amity, New York (xanthite): brown crystals, large; seldom cut.
Telemark, Norway (cyprine): fine blue masses with pink thulite.
Asbestos, Quebec, Canada: superb crystal groups and masses, apple green, sometimes colored deep green by Cr or pink by Mn.
Kenya: green and brown crystal fragments suitable for faceting.
Sanford, Maine: brown and green crystals and masses.
Wilui River, USSR: green crystals (known as wiluite).
Morelos, Mexico: green crystals associated with pink grossular in lake bed.
Quetta, Pakistan: fine green crystals; some transparent.
Comments: Idocrase is one of the lesser known and more beautiful collector gems. When properly cut it is as bright and attractive as the grossular garnets, which it so strongly resembles. The complexities of its chemistry lead to a huge range in properties and colors. Cuttable material is known from Italy (brown and green), Quebec (pale green, bright yellow), New York (brown), Pakistan (green), Kenya (brown and green).
Californite is a massive idocrase-grossular mixture reported first from California and later found in various other localities, such as Africa and Pakistan. The density is 3.25-3.32 and there is a strong 4610 band in its spectrum, which is easily distinguished from the chrome spectrum of jadeite.
Name: From the Greek words idos and krasis, meaning mixed appearance, because idocrase crystal forms resemble those seen on other species. Vesuvianite from Mt. Vesuvius, where the mineral occurs in small, perfect crystals.