Biotite
Optical Properties
In PPL
| Form | subhedral |
| Color | green-brown |
| Pleochroism | present |
| Relief | moderate |
| Cleavage | perfect 1 set |
| Fracture | - |
| Twinkling | absent |
In XPL
| Iso/Aniso | anisotropic |
| Interference Color | order-II,III bright |
| Extinction Angle | 0-5 degrees parallel to near parallel (bird's eye extinction) |
| Twinning | absent |