Amphibole is the general name for the hornblende family of minerals. These minerals can be divided into two sub-families: orthorhombic amphibole and monoclinic amphibole. These subfamilies can be further subdivided into anthophyllite, tremolite, actinolite, hornblende, riebeckite and glaucophane. Amphibole has a long columnar shape, and the aggregates are granular, fibrous or radiating. It has deep colours that vary from green, brown and tan to black. It has a vitreous lustre, a specific gravity of 3.0–3.5, and a Mohs hardness of 5–6. Amphibole is a common rock-forming mineral that is mainly found in metamorphic rocks. Hornblende is also an important mineral in intermediate and intermediate-acidic igneous rocks. Tremolite and actinolite with a dense blocky aphanitic texture are called soft jade (nephrite).