The Collaborative International Dictionary of English v.0.48:

Basanite \Bas"a*nite\, n. [L. basanites lapis, Gr. ba`sanos the
   touchstone: cf. F. basanite.] (Min.)
   Lydian stone, or black jasper, a variety of siliceous or
   flinty slate, of a grayish or bluish black color. It is
   employed to test the purity of gold, the amount of alloy
   being indicated by the color left on the stone when rubbed by
   the metal.
   [1913 Webster]