Rhodochrosite is a carbonate mineral with the chemical composition MnCO3 (manganese carbonate). In its (rare) pure form, it is typically a rose-red color, but can also be shades of pink to pale brown. It streaks white, and its Mohs hardness varies between 3.5 and 4.5. Its specific gravity is between 3.45 and 3.6. The mineral is formed by oxidation of manganese ore, and is found in South Africa, China and South America. It is Argentina's national gemstone, and was named as the official state gemstone by the U.S. state of Colorado in 2002. This photograph shows a rhodochrosite specimen on a matrix that originated from Peru.Photograph credit: John Harrison