Carbonate of Magnesia

There has been found at various places, principally in veins in serpentine rocks, an opaque mineral of a more or less earthy texture, and consisting chiefly of Magnesia, sometimes combined with carbonic acid; this has been called Native Magnesia and Magnesite: the varieties holding most carbonic acid have been distinguished by the chemical name of Carbonate of Magnesia: the purest kind is that from Hrubschitz in Moravia: it is compact, and hard enough to scratch calcareous spar. Native Magnesia, free from carbonic acid, but united to 30 per cent of water, is found at Hoboken, in New Jersey. Haüy says that in the present state of our knowledge we cannot easily decide whether the carbonate has been produced by the exposure of the native to the atmosphere; or whether they be originally distinct minerals. The substance exhibited in the present figure has been considered as Carbonate of Magnesia; it is, however, far from pure, but is rendered remarkable by being the matrix of beautiful insulated crystals, and groups, of blue Carbonate of Copper: it yields its Magnesia to sulphuric acid, in which it effervesces slightly : its texture is variable; sometimes it is quite loose, at others it is so hard as to yield with difficulty to the linger nail: it commonly assumes an irregular mammillated surface, and is of a pure white, partially stained greenish by copper, or yellowish brown by iron. From Chessy, near Lyons.