stephanite

from The Collaborative International Dictionary of English v.0.48

Stephanite \Steph"an*ite\, n. [So named after the Archduke
   Stephan, mining director of Austria.] (Min.)
   A sulphide of antimony and silver of an iron-black color and
   metallic luster; called also {black silver}, and {brittle
   silver ore}.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Brittle \Brit"tle\, a. [OE. britel, brutel, AS. bryttian to
   dispense, fr. bre['o]tan to break; akin to Icel. brytja, Sw.
   bryta, Dan. bryde. Cf. {Brickle}.]
   Easily broken; apt to break; fragile; not tough or tenacious.
   [1913 Webster]

         Farewell, thou pretty, brittle piece
         Of fine-cut crystal.                     --Cotton.
   [1913 Webster]

   {Brittle silver ore}, the mineral {stephanite}.
      [1913 Webster]