Synonyms for Crystal (same or very similar meaning)
WordNet sense 1 (colorless glass made of almost pure silica):
quartz, lechatelierite, quartz glass, vitreous silica
WordNet sense 2 (a rock formed by the solidification of a substance; has regularly repeating internal structure; external plane faces):
crystallization
WordNet sense 3 (a protective cover that protects the face of a watch):
watch glass, watch crystal
From the ODE community, based on WordNet
add/edit