Calcite group

Calcite (trigonal) Ca[CO₃]

	Colour: colourless Pleochroism: non pleochroic Habit: variety of habits, rhombohedron and scalenohedron forms Relief: moderate Cleavage, fracture: perfect rhombohedral cleavage Twinning: common polysynthetic twins
	Isotropic or anisotropic: anisotropic Extinction: straight Interference colours: 3rd order

Siderite (trigonal) Fe[CO₃]

	Colour: grey, yellow, brown Pleochroism: non pleochroic Habit: rhombohedron, sphericules (as seen on the left) and massive forms Relief: positive Cleavage, fracture: perfect rhombohedral cleavage
	Isotropic or anisotropic: anisotropic Extinction: straight Interference colours: 4th order

Kalcyt i Syderyt

Dolomite group

Dolomite (trigonal) CaMg[CO₃]₂

	Colour: colourless Pleochroism: non pleochroic Habit: variety of habits, rhombohedron and scalenohedron forms, fine-grained aggregates Relief: moderate Cleavage, fracture: perfect rhombohedral cleavage Twinning: occasional polysynthetic twins
	Isotropic or anisotropic: anisotropic Extinction: straight Interference colours: 3rd order