Sillimanite was named for the US geologist and professor, Benjamin Silliman (1779-1864) of Yale University. It is exceptionally rare, and a very beautiful stone. Sillimanite is found in two forms. One is clear and glassy, and the other is silky and fibrous. When it is found in its fibrous state, crystals occur in long slender prisms in parallel groups, resembling fibers, and this material is often called fibrolite. Collectors prize the fibrous crystals, but the glassy crystals are the ones used as gemstones.
Collectors love the stone's lively luster. Sillimanite can range in color from colorless to white, yellow, blue or brown. Crystals have a distinct pleochroism, showing pale yellowish green, dark green, and blue, from different angles. Some crystals demonstrate a cat's eye effect. When polished as cabochons, they glow mysteriously like a cats eye at night. These crystals make beautiful rings. Sillimanite is a brittle stone, rating a 6-7 on the hardness scale. It is a very difficult stone to cut; therefore only skilled lapidaries should attempt to do so. It is a vitreous, and transparent to translucent stone.
Sillimanite occurs typically in schists and gneisses produced by high-grade regional metamorphism. It also is found in metamorphic rocks and occasionally in pegmatites. Stones are generally found scattered among layers of metamorphic rocks, often around hot springs or areas of volcanic activity. The most sought after stones are from Ohngaing, Mogok, Burma (Myanmar). Gray to green varieties of the stone come from Sri Lanka, blue and violet varieties are found in Myanmar, and fibrolite is found in the United States, in Idaho. Large sillimanite stones can be found in Clearwater River Valley in Idaho and are often made into carvings. Other locations where sillimanite is found are Moldau and Schuttenhoten, in the Czech Republic, Chester, Middlesex County, Connecticut, and various locations around Italy, Germany, Brazil, Austria, and India.
Sillimanite is a great stone for someone who is trying to complete a task that seems overbearing and impossible to finish. We tend to get tired and lose excitement, when we work on something for too long. Wearing sillimanite allows the wearer to remember the felling of joy we get, when finishing a task that is important to us.
