Amphibole

Amphibole group

Amphiboles are double-chain silicates — hornblende, actinolite, tremolite, and glaucophane among them — forming prismatic to needle-like crystals in a wide range of igneous and metamorphic rocks. Two cleavages meeting near 124° distinguish them from pyroxenes. Collectors meet the group through gemmy actinolite, the dense felted form nephrite (one of the two true jades), and boldly colored blue glaucophane schists.