The Collaborative International Dictionary of English v.0.48:

Sillimanite \Sil"li*man*ite\, n. [After Benjamin Siliman, an
   American meneralogist.] (Min.)
   Same as Fibrolite.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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 bucholzite.
   [1913 Webster]