Hornblende
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 is an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate.
The general formula can be given as (Ca,Na)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2.
Compositional variances
Some metals vary in their occurrence and magnitude:
Physical properties
Hornblende has a hardness of 5–6, a specific gravity of 2.9–3.4 and is typically an opaque green, greenish-brown, brown or black color.
Its cleavage angles are at 56 and 124 degrees. It is most often confused with various pyroxene minerals and biotite mica, which are black and can be found in granite and in charnockite.
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