Hornblende
Hornblende is a complex inosilicate series of minerals. 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 minerals are common in igneous and metamorphic rocks.
| Hornblende | |
|---|---|
Hornblende crystal (dark green) about 35 mm long, with apatite (white) | |
| General | |
| Category | Silicate mineral |
| Formula (repeating unit) | Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2 |
| IMA symbol | Hbl |
| Crystal system | Monoclinic |
| Space group | C2/m |
| Identification | |
| Color | Black to dark green or brown |
| Crystal habit | Hexagonal/granular |
| Cleavage | Imperfect at 56° and 124° |
| Fracture | Uneven |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous to dull |
| Streak | Pale gray, gray-white, white, colorless |
| Specific gravity | 2.9 |
| Pleochroism | Strong |
| References | |
The general formula is (Ca,Na)2−3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2.
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