Magnesite

Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Mixed crystals of iron II carbonate and magnesite (mixed crystals known as ankerite) possess a layered structure: monolayers of carbonate groups alternate with magnesium monolayers as well as iron II carbonate monolayers. Manganese, cobalt and nickel may also occur in small amounts.