Carbonate · Uniaxial (−)
Dolomite in thin section
Like calcite, with changing relief and extreme birefringence (about 0.18). More commonly euhedral rhombs than calcite, and may be cloudy or stained by iron oxides.
Plane-polarized light
| Color | Colorless |
|---|---|
| Pleochroism (color change on rotation) | None |
| Relief | Changes on rotation |
| Cleavage | Rhombohedral |
| Shape | Rhombs, Anhedral / equant |
Cross-polarized light
| Maximum birefringence | about 0.180 |
|---|---|
| Highest interference color | Creamy high-order |
| Extinction | Symmetric to cleavage, Inclined |
| Twinning | None, Polysynthetic stripes |
Telling it apart
Calcite stains red with Alizarin Red S; dolomite stays unstained. Dolomite also has higher refractive indices.
Where you'll find it
Dolostone, dolomitic marble
Photo examples
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