Are the names of specific minerals capitalized?

No, the nouns form minerals are not capitalized unless it is the first Word in a sentence.

The best authority for capitalization of ordinary Words in running text is a recent edition of a major, authoritative dictionary, e.g. Webster's or Oxford. Browsing these dictionaries shows that the names of minerals are not capitalized. This is true even of the names of minerals that are derived from the (capitalized) proper names of places where they were discovered (e.g. bauxite, named after the village of Les Baux in France) or from the (capitalized) surnames of their discoverers, such as cohenite (named after German mineralogist Emil Cohen).