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Biotite
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Biotite mica properties
Biotite is a common phyllosilicate mineral within the mica group. The high content of iron ions gives it a dark hue. It is sometimes called "iron mica" because it is more iron-rich than phlogopite. It is also sometimes called "black mica" as opposed to "white mica" (muscovite) – both form in some rocks, and in some instances side-by-side.
- Chemical composition: K2(Mg,Fe)6(Al2Si6O20)(OH)4 - potassium iron magnesium aluminum silicate hydroxide
- Color: Black, dark brown, dark green, reddish black.
- Streak: White
- Hardness (Moh's Scale): 2,5 - 3,0
- Transparency: Translucent to opaque. Thin flakes will always be translucent if held up to the light.
- Luster: pearly
- Specific gravity: 2,7 - 3,1 g/cm3
- Crystal forms and aggregates: Crystals are in thick flakes, micaceous masses and groupings, and in tabular, foliated, flaky, and scaly forms. Crystals may also be elongated with one dimension flat, or stubby triangular or hexagonally shaped crystals. Also forms in prismatic barrel-shaped or tapered pyramid-shaped crystals composed of dense parallel plates, and as rounded modules of dense crystals.
Application of biotite:
- as insulating material in the electronics industry,
- in addition to plasters and paints
- after pulverization used as a non-stick surface coating on asphalt shingles and rolled roofing
- for products decorating
- for collection purposes
| Chemical Composition | ||
|---|---|---|
| Silicon dioxide | SiO2 | 41.58% |
| Alumina | Al2O3 | 11.76% |
| Potassium oxide | K2O | 10.86% |
| Ferric oxide | FeO | 8.29% |
| Magnesium oxide | MgO | 23.24% |
| Loss on ignition | H2O | 3.64% |
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