It is commonly found in continental rocks which are igneous in
origin. It often makes up the dark part of rocks which are composed of
light and dark crystals.
Hornblende has been used to estimate the depth of crystallization of
plutonic rocks. Those with low aluminum content are associated with
shallow depths of crystallization, while those with higher aluminum
content are associated with greater depths of crystallization.
Pretty big crystals because of high melting point so separate early and
have long time to grow.
is a common constituent of many igneous and metamorphic rocks such as
granite, syenite, diorite, gabbro, basalt, andesite, gneiss, and schist.
It is the principal mineral of amphibolites. Very dark brown to black
hornblendes that contain titanium are ordinarily called basaltic
hornblende, from the fact that they are usually a constituent of basalt
and related rocks. Hornblende alters easily to chlorite and epidote.