Vesuvianite

from WordNet (r) 3.0 (2006)

vesuvianite
    n 1: a green or yellow or brown mineral consisting of a hydrated
         silicate; it occurs as crystals in limestone and is used a
         gemstone [syn: {vesuvianite}, {vesuvian}, {idocrase}]

from The Collaborative International Dictionary of English v.0.48

Vesuvianite \Ve*su"vi*an*ite\, n. (Min.)
   A mineral occurring in tetragonal crystals, and also massive,
   of a brown to green color, rarely sulphur yellow and blue. It
   is a silicate of alumina and lime with some iron magnesia,
   and is common at Vesuvius. Also called {idocrase}.
   [1913 Webster]