What's That Rock?Biotite
A black or dark brown mica that peels into thin, shiny, flexible sheets. It is common in granite.
How to identify Biotite
- Peels into thin dark flakes
- Shiny, black, bendy sheets
- Soft: a knife scratches it
Often confused with
- Muscovitelight-colored mica
- Graphite
- Vermiculite
Is Biotite valuable?
Inexpensive.
What changes the price
- Common mineral: low value
- Large, clean, undamaged mica books are the collector piece
- Mostly an educational specimen
Uses
- Rock-forming mineral, dating rocks
Care
Flakes easily. Handle gently.
Identifying a stone from a description or a photo is an estimate. Many stones look alike. Ask an expert or a gem lab before you buy, sell or rely on an identification.
Updated October 2026