Virginia State Mineral
Kyanite is an aluminum silicate. Commonly a shade of blue and sometimes occurring as the most sought-after bright sapphire blue, kyanite can also occur as green, white, yellow, gray, black, or colorless. Color may be inconsistent throughout the mineral, as blotches or streaks are sometimes present.
This mineral is anisotropic, which means its properties can exhibit different values when measured in different directions. For example, kyanite’s hardness is approximately 4 to 4.5 on the Mohs scale when scratched parallel to the long axis of the crystal and approximately 6.5 when scratched or cut perpendicular to or across the long axis.
Kyanite is a polymorph with andalusite and sillimanite, meaning all three have the same chemical formula but different crystal structures. Together, these minerals constitute the sillimanite group. Kyanite can be distinguished from the others by its unique hardness, its long-bladed crystals, and its color. Kyanite is the only one of the three that occurs in its unique blue color.
A STATE SYMBOL
Kyanite Mining Corp. (KMC), the sole U.S. producer of kyanite, is located in Buckingham County, Virginia. This company produces kyanite from hard rock, open-pit mines and also operates two kilns to produce mullite, or calcined kyanite. While Virginia does not have an official mineral, kyanite is representative of the state’s geology and economy.
The name for this mineral comes from the Greek word κυανός (kuanos or kyanos), meaning "blue." The mineral most frequently occurs in blue.
FORMATION AND OCCURRENCE
Kyanite is often found in aluminum-rich metamorphic rocks, such as gneisses and schists, formed from sedimentary rocks. It is also found in quartz veins. In addition to its polymorphs, kyanite occurs in association with staurolite, biotite, talc, gedrite, mullite, and corundum.
Because kyanite is widespread, even for good crystals, only a few localities are listed here. Other significant deposits exist that are uneconomical to mine.
The steel-making industry consumes more than half of the kyanite used, and much of this mineral is also used in ceramics and glassmaking. Kyanite is also used to make refractories for nonferrous metals and to produce spark plugs, heating elements, and high-voltage electrical insulations.
Some specimens of kyanite are of gem quality. Since the mineral’s change in hardness is related to the cut, gem cutters can use this to their advantage. For this same reason, kyanite is best suited for use in earrings or pendants, as they are subjected to less stress than rings and bracelets.
It was once believed that a kyanite crystal suspended from a human hair could act as a compass needle. Kyanite was therefore popular with travelers to unknown territories. Some believe that kyanite can aid in self-expression and communication.
Two types of synthetic mullite (fused and sintered), superduty fire clays, and high-alumina materials are substitutes for kyanite in refractories. Principal raw materials for synthetic mullite are bauxite, silica sand, and kaolin and other clays.
Chemical Formula: Al2SiO5
Crystal Structure: Triclinic pinacoidal 1
Hardness (Mohs): 4.5-5 parallel to one axis; 6.5-7 perpendicular to that axis
Color: Blue; also green, white, grey, black
Transparency: Transparent to translucent
Luster: Vitreous to pearly
Cleavage:  perfect;  imperfect with 79° angle between
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press