Dolomite

Dolomite
Dolomite (white) with magnesite (yellowish) from Spain
General
Category	Carbonate minerals
Formula (repeating unit)	CaMg(CO3)2
Strunz classification	5.AB.10
Crystal system	Trigonal
Crystal class	Rhombohedral (3) H-M symbol: (3)
Space group	R3
Unit cell	a = 4.8012(1), c = 16.002 [Å]; Z = 3
Identification
Color	White, gray to pink
Crystal habit	Tabular crystals, often with curved faces, also columnar, stalactitic, granular, massive.
Twinning	Common as simple contact twins
Cleavage	Perfect on {1011}, rhombohedral cleavage
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	3.5 to 4
Luster	Vitreous to pearly
Streak	White
Specific gravity	2.84–2.86
Optical properties	Uniaxial (-)
Refractive index	nω = 1.679–1.681 nε = 1.500
Birefringence	δ = 0.179–0.181
Solubility	Poorly soluble in dilute HCl
Other characteristics	May fluoresce white to pink under UV; triboluminescent. Ksp values vary between 1x10−19 to 1x10−17
References

Dolomite (pronunciation: /ˈdɒləmaɪt/) is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO₃)₂. The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomitic rock type is dolostone.

Most probably the mineral dolomite was first described by Carl Linnaeus in 1768. In 1791, it was described as a rock by the French naturalist and geologist Déodat Gratet de Dolomieu (1750–1801), first in buildings of the old city of Rome, and later as samples collected in the mountains now known as the Dolomite Alps of northern Italy. Nicolas-Théodore de Saussure first named the mineral (after Dolomieu) in March 1792.

The mineral dolomite crystallizes in the trigonal-rhombohedral system. It forms white, tan, gray, or pink crystals. Dolomite is a double carbonate, having an alternating structural arrangement of calcium and magnesium ions. It does not rapidly dissolve or effervesce (fizz) in dilute hydrochloric acid as calcite does. Crystal twinning is common.