pyroxene

noun

Etymology: From French pyroxène, from pyro- + Ancient Greek ξένος (xénos, “stranger”).

1. Any of a group of crystalline minerals containing silicates of iron, magnesium and calcium.

   “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.”