Calcite

COLOR

Grey. Strong pleochroism. Polishes easily.

REFLECTANCE

Very low. About the same as quartz.

ANISOTROPISM

Strong but partly concealed by very light internal reflections.

TEXTURE

The mineral nearly always shows beautiful twin lamellae. These lamellae which often cut each other may be tectonically deformed. It is often xenomorphic and may occur as euhedral crystals frequently replaced by quartz. Calcite may replace dolomite but may also be replaced by the latter. In this case, it is easy to identify both minerals by etching them with dilute acids. Dolomite reacts negatively to etching whereas calcite is etched immediately.

ASSOCIATED MINERALS

All the minerals.

CRITERIA OF DETERMINATION

Very low reflectance, strong pleochroism and anisotropism, polysynthetic twins and rapid etching by dilute acids. Smithsonite and anglesite are also etched but are much more reflective and this is particularly striking in contact with quartz.

Source

ATLAS OF ORE MINERALS (P. Picot and Z. Johan)