What is "sillimanite"

Fibrolite \Fi"bro*lite\ (? or ?), n. [L. fibra a fiber + -lite: cf. F. fibrolithe.] (Min.) A silicate of alumina, of fibrous or columnar structure. It is like andalusite in composition; -- called also sillimanite, and bucholizite.

n. (context mineralogy English) A fibrous neosilicate mineral, polymorphic with andalusite and kyanite, with the chemical formula aluminum₂siliconoxygen₅.

Sillimanite is an alumino-silicate mineral with the chemical formula AlSiO. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Middlesex County, Connecticut, US.