Alto da Serra quarries, Rio Maior, Santarém, Portugal

CaCO₃

Crystal System: trigonal
Colour: colourless, white, yellow, red, orange, blue, green, brown or gray
Lustre: vitreous, sub-vitreous, resinous, waxy or pearly
Habitus: prismatic, scalenohedral, rhombohedral
Hardness: 3
Fracture: conchoidal
Cleavage: perfect - perfect on {10-11}
Density: 2.711 g/cm³ 
Origin and geological occurrence: it is the most stable polymorph of calcium carbonate. It is widespread in several geological environments. It occurs in sedimentary (e.g., limestone), metamorphic (e.g., marble), and rarely magmatic rocks (e.g., carbonatite). It is a common gangue mineral in hydrothermal veins. It occurs in cave where it forms speleothems.

www.mindat.org
Smorf link

Samples:

	5.3 Calcite Flattened rombohedral crystals of calcite. #carbonates
	5.4 Calcite Scalenohedral crystals of calcite. #carbonates
	5.5 Calcite   Pisolitic calcite. #carbonates
	5.6 Calcite  Rhombohedral calcite. #carbonates
	5.7 Calcite  #carbonates Scalenohedral crystals of calcite, covered by iron oxides. #carbonates
	5.8 Calcite Small scalenohedral colorless crystals of calcite. #carbonates
	5.9 Calcite Calcite showing a palisade structure. #carbonates