Sillimanite

Sillimanite is chemically named Aluminum Silicate and it shows polymorphism with minerals like Kyanite and Andalusite. A mineral which shares similar chemistry with other minerals but differs in their crystalline structure, is called a polymorph. The colors of this gemstone range from white, yellow green, brown, gray and colorless. The prism-shaped crystals possess an orthorhombic crystalline structure and they can be either transparent or translucent. Sillimanite has cleavage that is good and in a single direction, that is longitudinal.

Sillimanite was discovered in the year 1824 and get its name from an American professor of chemistry and geology, Mr. Benjamin Silliman. Sillimanite is a very rare trimorph and it has a common variety called fibrolite. Usually the bigger crystals of Sillimanite are hard with a hardness of 7.5 and the fibrous varieties are comparatively softer. The shine that the gemstone has is vitreous but the fibrous ones have a silky luster. It belongs to the class of Silicates and the subclass of Nesosilicates. Minerals like Feldspar, Andalusite, Quartz,Garnets, Kyanite and Biotite are associated with Sillimanite. The fibers of this mineral can be identified from asbestos because they are brittle. Sillimanite shows a white streak.

The formation of Sillimanite takes place at very high temperatures of 550 degrees centigrade and above. In the year 1977, Sillimanite was declared as the state mineral of Delaware where it is found in the Brandywine Springs and Hoope Reservoir areas. It brittleness makes it difficult to give it facets but the fibrous forms can be cut to resemble Cat's eye.

Uses of Sillimanite:

Sillimanite is a mineral with interesting properties which is used sparingly as a specimen of a mineral.

Places where Sillimanite is found: