Biotite is mainly derived from metamorphic rocks and occurs in other rocks, such as granite. The color of biotite is from black to brown, red or green, with a glassy luster.
Mica is usually a pseudo - six - or rhombic plate-like, flaky, columnar crystalline form that has the properties of being stripped to an elastic transparent sheet. Therefore, the shape of mica is generally considered as a sheet.
The shape is plate-like and columnar. Black mica has been widely used in various decorative coatings. Biotite single crystals are mainly short column or plate shape, the transverse section is hexagonal, and the aggregate is scaly. Brown brown or black color with the iron content increased and variable depth. Other optical properties and mechanical properties are similar to those of muscovite, with relative density 2.7~3.3. So, I choose C, six prismatic.
