Pyroxene Group - Orthorhombic Section, Enstatite, Bronzite, Hypersthene

The pyroxene Group includes a series of related metasilicates which have calcium, magnesium and ferrous iron as the important bases, also manganese and zinc. Further certain molecules contain the alkalies and aluminum and ferric iron. They may belong to either the orthorhombic, monoclinic or triclinic systems, but the crystals of the different species are closely similar in many respects.

Orthorhombic Section

Enstatite, Bronzite, Hypersthene
A group of orthorhombic members of the pyroxene group, enstatite, with small amounts of iron replacing the magnesium metasilicate, MgSiO₃; bronzite, the same as enstatite, with small amounts of iron replacing the magnesium; hypersthene, an iron –magnesium metasilicate, (Mg, Fe) SiO₃ Distinct crystals rare. Usually foliated massive with good cleavage; fibrous, etc. Color from white in enstatite to green and brown with increase in iron. Rock-making minerals; occurring like the monoclinic pyroxenes but much rarer. Found in basic igneous rocks, such as peridotite, gabbro. Etc.

Aegrite Or Acmite
A soda-ferric iron pyroxene NaFe”” (SiO₃)_2. Monoclinic. Slender prismatic crystals, often with steep terminations. Faces often imperfect prismatic cleavage with 93° angle. H. = 6-6.5. G. = 3.5-3.55.. Vitreous luster. Color brown or green. Translucent to opaque. Fusible at 3.5, giving yellow sodium flame. Fused globule slightly magnetic. A comparatively rare rock-making mineral found chiefly in rocks containing leucite or nephelite, as nephilite-syenite and phonolite.