Dolomite

Dolomite is a calcium magnesium carbonate, CaMg(CO₃)₂, and the type species of the dolomite group, related to ankerite and kutnohorite through isomorphous substitution of iron and manganese for magnesium. It crystallizes in the trigonal system, typically as rhombohedral crystals with characteristic curved, saddle-shaped faces, showing vitreous to pearly luster, perfect rhombohedral cleavage, and a hardness of 3.5–4. Colors range from colorless and white to yellow, brown, and, when enriched in manganese or cobalt, delicate pink to vivid magenta.

Classic localities include the Azcárate Quarry at Eugui, Navarra, Spain, source of some of the world's finest transparent, gemmy rhombohedra; the Tri-State district of Missouri, Oklahoma, and Kansas, famed for creamy curved crystals with galena and sphalerite; Brumado, Bahia, Brazil, known for large twinned crystals; and the Lengenbach quarry at Binntal, Switzerland. Exceptional cobalt-bearing material from the Kolwezi and Mashamba West mines in Katanga, Democratic Republic of Congo, produces intensely fuchsia to magenta specimens prized as some of the most striking pink minerals in existence. Other notable occurrences include Traversella and Brosso in Piedmont, Italy, the Trimouns talc mine in Ariège, France, and Freiberg, Saxony, Germany.

Collectors seek dolomite for its elegant rhombohedral habit, saddle-curved crystal faces, and unusual color range spanning from icy transparent Eugui specimens to shocking-pink Congolese cobaltoan dolomite, making it a versatile and visually rewarding species for systematic carbonate and locality collections alike.