Description and Characteristics
Biotite is a common phyllosilicate mineral within the mica group, primarily known for its perfect basal cleavage that allows it to be split into thin, flexible, and elastic sheets. The specimens from Madagascar are highly prized by collectors for their significant size and the structural perfection of their dark, tabular crystals.
| Chemical Formula | $K(Mg,Fe)_3AlSi_3O_10_(OH, F)_2$ |
|---|---|
| Luster | Vitreous to sub-metallic; pearly on cleavage surfaces. |
| Streak | White or light gray |
| Fracture | Uneven (rarely observed due to perfect cleavage) |
| Cleavage | Perfect basal (micaceous) |
| Hardness | 2,5-3 Mohs |
| Crystal System | Monoclinic |
Did you know...?
Its name honors the French physicist Jean-Baptiste Biot, who researched the unique optical properties of micas in 1816.
In the past, it was often referred to as "iron glass" due to its high heat resistance; it was commonly used for furnace windows and oven doors before modern industrial glass was developed.
Unlike Muscovite, Biotite contains high levels of iron and magnesium, which not only provide its dark hue but can also slightly interfere with compass readings in very large, massive specimens.
In the past, it was often referred to as "iron glass" due to its high heat resistance; it was commonly used for furnace windows and oven doors before modern industrial glass was developed.
Unlike Muscovite, Biotite contains high levels of iron and magnesium, which not only provide its dark hue but can also slightly interfere with compass readings in very large, massive specimens.
New-Age Properties
Known as the "Stone of Vision," Biotite is used to enhance mental clarity and promote self-reflection. It is believed to help process information rationally and assist in releasing obsolete thought patterns, grounding the user while expanding their consciousness.