US Virgin Islands Territorial Gemstone
Prehnite STATUS Unofficial DESCRIPTION Prehnite is a translucent mineral that can be colorless to gray to yellow, yellow-green, apple green, mint green, light brown, blue, or white. It often occurs in a shade of green unique to prehnite. It is a hydrated silicate of calcium and aluminum. STATE SYMBOL Although the U.S. Virgin Islands do not have an official gemstone, prehnite represents the territory's geology and economy well, as the mineral occurs on all three islands. Prehnite occurs as spongy crystals in association with the mineral wairakite in the Judith Fancy Formation on St. Croix, in association with pumpellyite on St. John, and at Nadir on St. Thomas. NAME ORIGIN Prehnite is the first mineral to be named for an individual, and also the first to be named and described from South Africa, a country that today enjoys a thriving gemstone industry. Colonel Hendrik von Prehn (1733-1785), governor of the Dutch colony at the Cape of Good Hope from 1768 to 1780 and also a mineralogist, was the first to discover the mineral. He took it back to Europe, and the stone was posthumously named for him in 1788. FORMATION AND OCCURRENCE Prehnite is a secondary mineral in volcanic rocks rich in iron and magnesium. It occurs at sites of low-grade metamorphic or hydrothermal activity, in veins and cavities of basaltic and igneous rock. It forms rough, thick crusts of crystals over laumonite crystals. Prehnite is revealed when the laumonite is washed away. GEOGRAPHIC DISTRIBUTION South Africa: Cape of Good Hope, Cape Province Namibia: Copper Valley, Brandberg Mountains France: La Combe-de-la-Selle, near Bourg d’Oisans, Is¨¨re Austria: Habachtal, Salzburg, and Ankogel Germany: Radauthal, near Harzburg, Harz Mountains Italy: Campitello, Val di Fassa, Trentino-Alto Adige Switzerland: Comperio, Graub¨¹nden, and St. Gotthard, Ticino United Kingdom: Scotland United States: Paterson, Passaic County, New Jersey; Bergen Hill, Hudson County, New Jersey; Fairfax quarry, Centreville, Fairfax County, Virginia; Roncari quarry, East Granby, Hartford County, Connecticut; Hampden quarry, West Springfield, Hampden County, Massachusetts; Upper Peninsula/Lake Superior region, Michigan Canada: Jeffrey mine, Asbestos, Quebec India: Khandivali quarry, Bombay, Maharashtra, India Australia: Coonabarabran, Warrumbungle Ranges, and Emu quarry, Prospect Hill, near Sydney, New South Wales Antarctica: Rennick Glacier, North Victoria Land USES Appreciated as an interesting collection mineral, prehnite is becoming more common as a gemstone. Prehnite a rare gem until about the 1980s, when large deposits were found in Australia. The stone is now more available and consequently more affordable. It may still be somewhat difficult to find in local jewelry stores, however. The stone has traditionally been cut as a cabochon, carved, or cut and polished as an ornament. More recently, faceted prehnite has become popular in jewelry, as have prehnite beads. Higher quality faceted stones and clear mint green specimens are the most prized and command the highest prices. LEGEND Prehnite is said to encourage composure, forgiveness, and acceptance. Some consider it a stone of unconditional love, and is believed to be an excellent stone for meditation. Some people also believe that prehnite helps relieve nightmares and many phobias.	Prehnite Unusual Prehnite Shapes Prehnite Close Up Isolated Prehnite PREHNITE FACTS Group: Silicates  Chemical Formula: Ca2Al(AlSi3O10)(OH)2 Crystal Structure: Orthorhombic-Pyramidal (mm2) Hardness (Mohs): 6-6.5 Color: Colorless to gray to yellow, yellow-green or white Transparency: Translucent Luster: Vitreous, pearly Birefringence: ¦Ä = 0.021 - 0.033 Refractive Index: n¦Á = 1.611 - 1.632 n¦Â = 1.615 - 1.642 n¦Ã = 1.632 - 1.665 Density: 2.8-2.95 Streak: White Cleavage: Distinct/good, good on {001}, poor on {110} Fracture: Irregular/uneven
	Some data courtesy of the Mineralogical Society of America Author: World Trade Press