Magnesite crystals are carbonate minerals of the trigonal crystal system, usually in the form of crystalline or cryptocrystalline compact blocks. The latter is also called porcelain-like magnesite. It is white or off-white, and iron-containing is yellow to brown. , Glass luster. The composition of magnesite is mainly MgCO3, and iron and manganese are often substituted for magnesium, but the iron content of natural magnesite is generally not high. With complete rhombohedral cleavage, porcelain-like magnesite has a shell-like fracture. The Moss hardness is 3.5-4.5, and the specific gravity is 2.9-3.1.