THE MINERAL SILLIMANITE
- Chemistry: Al2 SiO5, Aluminum Silicate
- Class: Silicates
- Subclass: Nesosilicates
- Uses: in the manufacture of spark plugs etc, rarely as a gemstone and as mineral specimens.
(also called Bucholzite) is a polymorph with two other minerals:
A polymorph is a mineral that shares the same chemistry but a different crystal structure with another, or other, minerals.
Sillimanite is the rarest of the three trimorphs
A variety of sillimanite is called "fibrolite".
It is a common fibrous massive form.
Sillimanite is the official state mineral of Delaware.
- Color is white, brown and green.
- Luster is silky when fibrous or vitreous otherwise.
- Transparency crystals are transparent to translucent.
- Crystal System is Orthorhombic; 2/m2/m2/m
- Crystal Habits include rare prismatic crystals but mostly fibrous masses.
- Cleavage is good in one direction lengthwise.
- Fracture is splintery.
- Hardness is 7.5 in large crystals but more fibrous forms are softer.
- Specific Gravity is approximately 3.2+ (above average)
- Streak is white.
- Associated Minerals are
- Other Characteristics: fibers are brittle distinguishing them from asbestos minerals.
- Notable Occurrences include Brazil, New England area and many European sites.
- Best Field Indicators are crystal habit, color, brittleness and hardness if not