Minerals & Gemstone 480x104
Minerals & Gemstone 480x104
Minerals V2 banner 160x600



Advertising Information

Fibrous While Sillimanite

The Mineral sillimanite




Sillimanite is named in honor of Benjamin Silliman (1779-1864), noted chemist and the earliest professor to teach mineralogy at Yale University. Silliman was also the father in law of noted mineralogist and author James Dwight Dana.
Chemical Formula Al2SiO5
Composition Aluminum silicate
Color Gray, brown, yellowish-gray, white. Rarely colorless, light pink, or light purple.
Streak Colorless
Hardness 6.5 - 7.5
Crystal System Orthorhombic
Crystal Forms
and Aggregates
Most often fibrous, sometimes with radiating crystal sprays embedded in matrix. Also columnar, massive, compact, and as rounded waterworn crystals and crystal masses. Rarely as prismatic crystals.
Transparency Transparent to translucent
Specific Gravity 3.2 - 3.3
Luster Vitreous, silky
Cleavage 1,1
Fracture Uneven, splintery
Tenacity Brittle
In Group Silicates; Nesosilicates
Striking Features Crystal habits and hardness
Environment In metamorphosed schists and gneisses. Rarely in granite pegmatites.
Rock Type Metamorphic
Popularity (1-4) 3
Prevalence (1-3) 3
Demand (1-3) 2


Sillimanite ON EBAY
OTHER NAMES
Fibrolite

POLYMORPHS
Kyanite


USES
The rare transparent Sillimanite crystals from Burma, Sri Lanka, and India are valued as important rare collector stones, and are occasionally cut into exquisite gemstones for collectors. Compact masses of Sillimanite were once used by Native Americans of the American Southwest to fashion tools.

NOTEWORTHY LOCALITIES
Unusual prismatic and waterworn transparent crystals of Sillimanite come from Mogok, Burma (Myanmar); and from the Ratnapura District, Sri Lanka. Orissa, India, is another uncommon source for transparent crystallized Sillimanite. 

In the U.S., brownish fibrous crystal groupings of Sillimanite have come from Chester, Middlesex Co., Connecticut. Also in Connecticut are the old classic locality of Norwich, New London Co.; and Willimantic, Windham Co., where small crystals in matrix were found. Fibrous masses of Sillimanite come from Brandywine Springs, New Castle Co., Delaware; and dark brown crystals crystal sprays from Oconee Co., South Carolina. Gray Sillimanite masses are found in Natrona Co., Wyoming.

COMMON MINERAL ASSOCIATIONS
Quartz, Biotite, Almandine, Plagioclase

DISTINGUISHING SIMILAR MINERALS
Tremolite - Lower hardness, often fluorescent.
Chrysotile - Much lower hardness, greasy feel, and flexible.
Dumortierite - Usually in a more blue or violet color.


sillimanite PHOTOS
 
ADDITIONAL RESOURCES
 
DISCUSSIONView Forum | Post to Forum
Have a question about Sillimanite? Visit our Q&A Community and ask the experts!
PAGE SPONSOR  

To sponsor this page, click here.

Let us know how we can update this page
(Click for more details)
We strive for accurate content and locality information. If you feel any of the content is incorrect, or if you feel we are missing vital locality information, please fill out the form below so we can update the site. If you are requesting a locality be added, please only include significant locality occurences for the mineral.