Dolomite is a mineral with a hardness of 4 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of calcium magnesium carbonate, their full chemical compound being CaMg(CO3)2.
Dolomite is similar to calcite and sits along side it in limestone. It usually occurs as a secondary mineral, formed by the reaction of magnesium-bearing fluids seeping through the limestone. It may be colorless, or white to cream and even yellow brown, sometimes pale pink. It has a vitreous luster and is translucent.
The faces of dolomite crystals are often curved, sometimes so acutely that the crystals become saddle-shaped. Its crystals are richly faceted, embedded and surface growing, mostly composed of rhombohedral forms, occasionally twinned. Aggregates are granular, columnar, sparry, and porous.
It is semi-hard, not very heavy, is fragile and has perfect rhombohedral cleavage.
It slowly dissolves with effervescence in cold, dilute, hydrochloric acid, but more quickly when heated.
It is a rock-forming mineral in dolomitic limestones, together with calcite, is a widespread gangue mineral in hydrothermal veins, especially accompanying galena and sphalerite, and is associated with talc schists and serpentinite. It is formed under diagenetic conditions by the action of seawater on calcareous mud or by organogenetic formation.
The finest crystals are found in Brosso and Traversella, Piedmont (Italy), where ankerite specimens have also been found, the Binnenthal (Switzerland), the Freiberg and Schneeberg Mines (Germany), Cornwall (England), Joplin, Missouri (USA), St. Eustache (Quebec, Canada), Navarra (Spain), Bahia (Brazil), and Guanajuanato (Mexico).
Beautiful ankerite crystals also occur in porphyry cavities at Cuasso al Monte (Varese, Italy), and in the Binnenthal. Pink, massive kutnohorite is found in the Kutnohora locality (Bohemia, Czechoslovakia), at Franklin, New Jersey (USA), Providencia (Mexico), and Nagano (Japan).
The variety "pearl spar" is white, grey, or pale brown, with a pearly luster.
Brown, rhomb, or bitter-spar are iron-bearing varieties, colored brown by the presence of ankerite, a cross between dolomite and siderite.
It is named after the French mineralogist, D. de Dolomieu, who first described the mineral in 1791. The Dolomites in the S.Calcareous Alps were then named after the mineral. The synonym "bitter spar" which is today rarely used was coined in reference to other Mg-minerals which do indeed taste bitter, but dolomite itself does not taste bitter.
Dolomite rocks are useful building materials (as structural and ornamental stone, and for special cements) and refractories (materials that can withstand high temperatures) as fire-resistant stones, particularly for furnace linings. The mineral is used for the extraction of metallic magnesium, fluxes and slag in the iron and steel industry, and in the chemical industry, for preparing magnesium salts. It is distinguished from calcite by its reluctance to dissolve in dilute acid.