staurolite
noun
stau·ro·lite ˈstȯr-ə-ˌlīt 
: a mineral consisting of a basic silicate of iron and aluminum in prismatic orthorhombic crystals often twinned so as to resemble a cross
staurolitic
ˌstȯr-ə-ˈli-tik
adjective 
Word History
Etymology
French, from Greek stauros cross + French -lite — more at steer
First Known Use
circa 1815, in the meaning defined above