Calcite

Sample of subhedral rhombohedron Calcite crystals that are pale yellow with a vitreous lustre. Calcite (CaCO3) can be white, colourless or pale shades of grey, yellow, red, green, blue or brown and black when impure. Lustre is vitreous or dull and streak is white. Hardness is 3 and cleavage is perfect in three directions forming a rhombohedron. Calcite usually occurs as rhombohedrons, scalenohedrons and prisms. Calcite can also be tabular, acicular, cleavable, granular, compact, stalactitic, oolitic or earthy.