Defines an important group of generally dark-colored rock-forming inosilicate minerals generally containing ions of iron and/ or magnesium in their structures.

In chemical composition and general characteristics they are very similar to the pyroxenes and, like them, fall into three series according to their system of crystallization.

The  primary difference between amphiboles and pyroxenes are that

(i) they contain hydroxl ions (OH)

(ii) the basic structure is a double chain of tetrahedra (as opposed to the single chain structure of the pyroxene).

Amphiboles are minerals of either original or secondary origin; in the former case occurring as constituents (hornblende) of igneous rocks, such as granite, diorite, andesite and others.

Those of secondary origin have either been developed in limestones by contact metamorphism (tremolite) or have resulted by the alteration of other ferromagnesian minerals such as augite by dynamo-metamorphism (actinolite).

Pseudomorphs of amphibole after pyroxene are known as uralite.