13 Mayıs 2013 Pazartesi

U.S. Virgin Islands Territorial Mineral

U.S. Virgin Islands Territorial Mineral


Wairakite is composed of calcium, hydrogen, oxygen, aluminum, and silicon. Calcite, quartz, and chlorite impurities may be present. Wairakite forms a series with the mineral analcime. Wairakite occurs as a colorless to white mineral that can be transparent to translucent and sometimes nearly opaque.
Wairakite occurs in the Judith Fancy Formation on St. Croix and at Nadir, St. Thomas. While the U.S. Virgin Islands do not have an official mineral, wairakite is representative of the territory’s geology.
This mineral was named for the town of Wairakei in the Taupo Volcanic Zone on the North Island of New Zealand. Wairakite was first discovered there in 1955.
Wairakite forms in pores and cavities in rocks in geothermal areas, deposited from hydrothermal fluids. It also forms in sandstones and breccias, glassy and welded tuffs, limestone, and clay. The Judith Fancy Formation on St. Croix, U.S. Virgin Islands, is composed of low-grade metamorphic rock of marine origin.
Wairakite typically forms after the deposition of epidote, prehnite, and later, anhydrite and calcite. In addition to these minerals, wairakite is also associated with andesine, clinozoisite, aragonite, and quartz. Wairakite reacts with water to form prehnite, montmorillonite, and quartz. The mineral may replace feldspar.
Some of the known localities are listed here.
  • New Zealand: on North Island, at Wairakei, near Lake Taupo; and in the Tui mine, Te Aroha, Auckland
  • United States: The Geysers, Sonoma County, California; near Rosamond, Kern County, California; Yellowstone National Park, Wyoming; and Mt. Rainier National Park, Pierce County, Washington
  • U.S. Virgin Islands: St. Thomas and St. Croix
  • Canada: Buttle Lake area, Vancouver Island, British Columbia
  • Japan: Seigoshi mine, Shizuoka Prefecture; Toi, Shizuoka Prefecture; Kawazu, Shizuoka Prefecture; Koriyama, Fukushima Prefecture; Onikobe, Miyagi Prefecture; Yugami district, Fukui Prefecture; Hikihara, Hyogo Prefecture; and at a number of other localities
Wairakite is a member of the zeolite group. Zeolites are hydrated aluminum silicates that form in volcanic rock cavities and are used for their molecular sieve properties, in addition to their use as water softening agents and absorbents. Wairakite has been synthesized at high temperatures using the minerals kaolin, calcite, and quartz in powdered form.
State Mineral
Group: Zeolite
Chemical Formula: CaAl2Si4O12·2(H2O)
Crystal Structure: Monoclinic-prismatic
Hardness (Mohs): 5.5-6 
Color: Colorless, white
Transparency: Transparent to translucent
Luster: Vitreous to dull
Pleochroism: None
Density: 2.26
Streak: White
Cleavage: [100] distinct
Fracture: Brittle 
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press

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