Named after professor Silliman of Yale University, USA, sillimanite is also known as “fibrolite” because of the distinct fibers present within. Sillimanite is found in metamorphic rocks and sometimes in pegmatite.

Locations:

Blue and violet stones are found in Burma. Greenish gray stones are found in Sri Lanka. Other localities include USA, the former Czechoslovakia, Italy, India, Brazil and Germany.

Chemical Composition: Aluminum Silicate
Crystal Structure: Orthorhombic
Hardness: 7.5
Specific Gravity: 3.25
Refractive Index: 1.66-1.68
Colors: Blue to green, pale yellowish green, dark green and blue from different angles.
Luster: Vitreous