Hornblende is a common mineral group of the earth and is oftern referred to as the pure rock variant Hornblendite. It is relatively hard and forms a major constituent of the amphibole group, which contain iron, magnsesium, silicon, and oxygen and hydroxyl. Hornblende is usually darker in color and opaque; as a cabachon or trillion it produces a very substantial semi-precious gemstone.
| Chemical Formula | Ca(2)(Mg,Fe^2+,Fe^3+,Al((s)(Si,Al((8)O(22)(OH)(2) |
| Color | Dark green, dark blue, dark gray, colorless |
| Hardness | 5 - 6 |
| Crystal System | Monoclinic |
| Refractive Index | 1.615Â -Â 1.730 |
| SG | 2.9Â -Â 3.4 |
| Transparency | opaque |
| Double Refraction | 0.020 |
| Luster | Vitreous, submetallic, dull |
| Cleavage | 2,2 - prismatic |
| Mineral Class | Silicate |
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