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Sheets of biotite are flexible. They can be bent and go back to their original shape. |
Mineral Characteristic | What the mineralogists say | Kid's Guide: What it REALLY means! |
Chemical Symbol | K2(Mg,Fe)3AlSi3O10(OH,O,F2)2 | It has oxygen, silicon, magnesium, potassium, iron, aluminum, fluorine, and hydrogen in it. |
Color | Dark green, brown, or black | These are the usual colors. When it has a lot of iron in it, biotite is a darker color. |
Streak | White | If you crushed this mineral, it would become white dust. |
Transparency | Transparent to translucent | Depending on the piece, light will pass through it. It is easier to understand that sometimes you can see through it clearly and other times it would be blurry. |
Luster | Glossy, vitreous, pearly | If you shine a light on this mineral, it would look glossy or have a shine like pearls have. |
Cleavage | Perfect in one direction | When it is broken, biotite perfectly splits into sheets or layers that can be split even more with a fingernail. |
Fracture | Uneven when seen | It does not break into small pieces because it splits evenly into sheets first. |
Magnetism | None | It will not attract, or be attracted to, a magnet. |
Hardness | 2.5 | It is not very hard. Sheets of biotite are flexible and can bend. |
Specific gravity | 3.0 | Compared to an equal volume of water, this is slightly heavier. If you held it in your hand, it would seem to be a little heavier than it looks like it would be compared to its size. |
Crystal Shape | Monoclinic |
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