1 example sentence using tourmaline.
Tourmaline used in a sentence
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