Silicates: Biotite-Phlogopite

Composition: K₂(Mg,Fe)_6-4(Fe,Al,Ti)_0-2(Si_6-5Al_2-3O₂₀)(OH,F)₄; the name biotite is used for the dark-colored iron-rich variety, the name phlogopite is used for the pale-colored iron-poor variety

Crystal system: Monoclinic; lamellar masses or small flakes

5.6.1
cleavable biotite
Harts Range central Australia

Properties:

• Vitreous lustre
• Brown, green, or black color depending on iron content
• White to grey streak
• Knife scratches very easily; fingernail barely scratches cleavage faces (Mohs Hardness 2.5)
• Average to above average density depending on iron content
• Single perfect cleavage
• Cleaves rather than fractures
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

5.6.2 cleavable biotite Harts Range central Australia	5.6.3 cleavable biotite Harts Range central Australia

5.6.4 cleavable biotite Harts Range central Australia	5.6.5 cleavable biotite Harts Range central Australia

5.6.7
cleavable biotite
Harts Range central Australia

Biotite and phlogopite occur in metamorphic rocks, many igneous rocks and hydrothermal vein and replacement ore deposits.

5.6.8 cleavable biotite Harts Range central Australia	5.6.9 cleavable biotite Harts Range central Australia

Phlogopite is a significant industrial mineral with similar use to muscovite in the manufacture of paints, paper, cosmetics, insulators and many other materials.

5.6.10
cleavable biotite
Harts Range central Australia