Sillimanite was named after Yale chemistry professor Benjamin Silliman. It is related to kyanite and andalusite, and comes in a variety of shades, ranging  from blue or blue-green to yellow, yellow-green, gray-green, or brown, and almost colorless, especially in thin slices. Some forms of Silliamnite, known as "fibrolite" look like bundles of fiber. The stone can be color-enhanced, resulting in beautiful patterns!

Sillimanite is found as far apart as Brandywine Springs in New Castle County, Delaware, United States, and in Sri Lanka.

Although sillimanite is becoming better known to the gem world, it has mainly been used in the glass industry.