Tourmaline in a sentence as a noun

That mineral is tourmaline. I think if you check that boulder and others like it you could rule out a natural origin if you find no evidence of tourmaline in the boulders.

Tourmaline definitions

noun

a mineral that is a complex borosilicate and hydroxide of aluminum containing iron and magnesium and calcium and lithium and sodium; it is usually black but occurs in transparent colored forms that are used as gemstones