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.
FORMATION AND OCCURRENCE
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.
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.
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
Cleavage:  distinct
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press