Glossary of Terms
Group of minerals that contain iron, magnesium, silicon, oxygen, and hydroxyl (OH). Amphiboles may also contain calcium, sodium, and lithium. The amphiboles have prismatic cleavage with an angle of 56° and 124°, which distinguishes it from the pyroxenes, which have an angle of 87° and 93° (almost perpendicular). The amphiboles are very similar to the pyroxenes, and the minerals belonging to each Group often cannot be distinguished by ordinary methods. Generally, though, the amphiboles occur in longer, thinner crystals than the pyroxenes. The pyroxenes contain the same elements that the amphiboles do, except they lack hydroxyl, which alters both physical and chemical properties.
The amphibole group is in the inosilicates subdivision of the silicates group.