Staurolite /(sta̤"rō̇*līt)/

Stau·ro·lite

Staurolite

n.
  1. A mineral of a brown to black color occurring in prismatic crystals, often twinned so as to form groups resembling a cross. It is a silicate of alumina and iron, and is generally found imbedded in mica schist. Called also granatite, and grenatite. (Min.)