pyroxene

pyroksiini, pyrokseeni puhekieltä Any of a group of crystalline minerals containing silicates of iron, magnesium and calcium.
2004, (w), The Earth, Folio Society 2011, p. 10:

By the pathside, there are occasional large boulders that shown black crystals the size of a fingernail; these are pyroxene minerals that had time to crystallise out deep within the chamber of liquid rock – or magma – beneath the volcano.