Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Siderite is a mineral composed of iron carbonate FeCO3. It takes its name from the Greek word sideros, iron . It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Both magnesium and manganese commonly substitute for the iron. Siderite has Mohs hardness of 3.5-4, a specific gravity of 3.8, a white streak and a vitreous or pearly luster. Its crystals belong to the hexagonal system, and are rhombohedral in shape, typically with curved and striated faces. It also occurs in masses. Color ranges from yellow to dark brown or black, the latter being due to the presence of manganese (sometimes called manganosiderite).