Rhodochrosite
Catamarca Province, Argentina
This specimen measures 8.5cm in diameter
Rhodochrosite MnCO3
Carbonate; manganese carbonate, often contains calcium, iron, magnesium, and zinc
Color and Luster: Pink, rose-red, dark red, brown; darkens on exposure to atmosphere; vitreous, pearly; streak white
Hardness: 3.5-4
Cleavage: Perfect in three directions, forming a rhombohedron
Fracture: Uneven, brittle
Crystals: Hexagonal; most often in rhombohedrons, also cleavage masses, granular, compact, botryoidal, incrusting; distinct crystals uncommon
Photo by Lance Kearns
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals