Identification Tips
1. Biotite, like the other types of mica, consist of seemingly endless, flexible, transparent sheets. Therefore, mica crystals are referred to as "books." You can separate the sheets easily with your fingernail
2. Biotite possesses a black to dark brown sheen and this distinguishes it from other common mica types. Light passing through a single thin sheet of biotite resembles light passing through a weak sunglass lens.
