Hornblende is a complex inosilicate series of minerals (ferrohornblende – magnesiohornblende). It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole.
Hornblende crystal (dark green) about 35 mm long, with apatite (white)
|Ca2(Mg, Fe, Al)5 (Al, Si)8O22(OH)2|
|Crystal system||Monoclinic unknown space group|
|Color||Black to dark green or brown|
|Cleavage||Imperfect at 56° and 124°|
|Mohs scale hardness||5–6|
|Luster||Vitreous to dull|
|Streak||Pale gray, gray-white, white, colorless|
The general formula can be given as (Ca,Na)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2.
Some metals vary in their occurrence and magnitude:
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.
Other minerals in the hornblende series include:
- List of minerals – A list of minerals for which there are articles on Wikipedia