Magnesite is often composed of iron and manganese instead of magnesium, but natural magnesite has low iron content. Magnesite crystals are triangular carbonate minerals, usually crystalline or cryptocrystalline dense bulk, the latter is also known as porcelain magnesite, white or gray-white, iron-bearing yellow to brown, glass luster. It has a complete rhombohedral cleavage, and a porcelain like magnesite has a shell like fracture. Moss hardness is 3.5 to 4.5, and the specific gravity is 2.9 to 3.1.