Glossary of Terms
Group of inosilicates that contain iron, magnesium, silicon, and oxygen. They may also contain calcium, sodium, and lithium. The pyroxenes have prismatic cleavage, and one can note the angle of 87° and 93° (almost perpendicular), which distinguishes them from the amphiboles which are at 56° and 124°.
The pyroxenes are very similar to the amphiboles, and the minerals belonging to each group are sometimes indistinguishable by ordinary methods. Generally, though, the pyroxenes occur in shorter, stubbier crystals than the amphiboles. The amphiboles contain the same elements as the pyroxenes, except they have hydroxyl (OH) in their structure, which alters both their physical and chemical properties.