Silicates: Hornblende

Composition: (Na,K)_0-1Ca₂(Mg,Fe,Al)₅(Si,Al)₈O₂₂(OH,F)₂

Crystal system: Monoclinic; prismatic crystals six-sided in cross section, also massive and as irregular grains

5.13.1
cleavable hornblende

Properties:

• Vitreous lustre
• Green, brown or black color
• White to grey streak
• Knife does not scratch (Mohs Hardness 6)
• Above average density depending on iron content
• Two cleavages not at right angles to each other
• Cleaves rather than fractures
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Hornblende occurs in medium grade metamorphic rocks, many igneous rocks and some hydrothermal replacement ore deposits.

5.13.2 cleavable hornblende	5.13.3 cleavable hornblende