- A common mineral embracing many varieties varying in
color and in composition. It occurs in monoclinic crystals; also
massive, generally with fibrous or columnar structure. The color varies
from white to gray, green, brown, and black. It is a silicate of
magnesium and calcium, with usually aluminium and iron. Some common
varieties are tremolite, actinolite, asbestus, edenite, hornblende (the
last name being also used as a general term for the whole species).
Amphibole is a constituent of many crystalline rocks, as syenite,
diorite, most varieties of trachyte, etc. See Hornblende.