Mica · Biaxial (−)
Muscovite in thin section
Colorless flakes with one perfect cleavage, bright 2nd- to 3rd-order colors (birefringence about 0.035–0.042) and mottled 'bird's-eye' extinction typical of micas.
Plane-polarized light
| Color | Colorless |
|---|---|
| Pleochroism (color change on rotation) | None |
| Relief | Moderate, Changes on rotation |
| Cleavage | One |
| Shape | Flakes |
Cross-polarized light
| Maximum birefringence | about 0.038 |
|---|---|
| Highest interference color | 2nd-order blues, greens, 3rd-order |
| Extinction | Parallel, Bird's-eye |
| Twinning | None |
Telling it apart
Muscovite is distinguished from biotite by its lack of color.
Where you'll find it
Granite, pegmatite, schist, phyllite
Photo examples
Alex Strekeisen · Alex Strekeisen (sericite) · Search Wikimedia Commons
Photos open on the source sites.
Identify an unknown grain Read interference colors Practice mineral ID
Related minerals
Sources
OpticMin, ATHENA, Univ. of Geneva (P. Perroud) · Alex Strekeisen thin-section collection · Distinguishing features of minerals (UT Arlington) · MIT OCW 12.109 amphibole lab · SEPM Strata: carbonate staining · Wikipedia mineral pages (infobox optical data) · Athabasca University rocks and minerals · Smith College petrography: perthite