Rhodocrosite is a manganese carbonate mineral. Its chemical
composition is MnCO. In its purest form it is a transparent rose red,
but this is fairly rare. It can also be formed in stalactites. This
form can be sliced revealing circular layers of rose and pink to milky
white. These lighter colours are formed when the manganese is replaced
by calcium, manganese or zinc. The depth of colour from red to pink
depends on the amount of substitution.