Short answers, pulled from the story.
Pyroxene comes from the Ancient Greek words for fire and stranger. The minerals were named for appearing as crystals embedded in volcanic glass, where early observers wrongly assumed they were impurities in the glass.
Pyroxenes are single-chain inosilicate minerals built from parallel chains of silica tetrahedra. Each silicon ion sits inside four oxygen ions and shares two oxygens with neighboring silicon ions along the chain. The chains are bonded together by metal cations, and the relatively weak outer bonding gives pyroxenes their characteristic cleavage.
Clinopyroxenes are pyroxenes that crystallize in the monoclinic system, including aegirine, augite, diopside, jadeite, pigeonite and spodumene. Orthopyroxenes crystallize in the orthorhombic system and include enstatite, hypersthene and ferrosilite.
Twenty pyroxene mineral names are recognized by the International Mineralogical Association's Commission on New Minerals and Mineral Names. Another 105 previously used names have been discarded.
Pyroxene cannot exceed 50 mol.% calcium because the calcium ion cannot occupy the Y site in the structure. The related mineral wollastonite has the formula of the hypothetical calcium end member but is classified as a pyroxenoid because of structural differences.
Pyroxene and olivine minerals make up most of Earth's upper mantle. Pyroxene and feldspar are also the major minerals in basalt, andesite and gabbro rocks.