The Collaborative International Dictionary of English v.0.48:

Aragonite \A*rag"o*nite\, n. [From Aragon, in Spain.] (Min.)
   A mineral composed of calcium carbonate and identical in
   composition with calcite, but differing from it in its
   crystalline form and some of its physical characters.
   [1913 Webster]

WordNet (r) 3.0 (2006):

aragonite
    n 1: a mineral form of crystalline calcium carbonate; dimorphic
         with calcite