MAGNESITE  , a

mineral consisting of magnesium carbonate, MgCO3, and belonging to the calcite group of rhombohedral carbonates . It is rarely found in crystals or crystalline masses, being usually compact or earthy and intermixed with more or less hydrous magnesium silicate (meerschaum) . The compact material has' the appearance of unglazed porcelain, and the earthy that of chalk . In colour it is usually dead white, some-times yellowish . The hardness of the crystallized mineral is 4; sp. gr . 3.1 . The name magnesite as originally applied by J . C . Delametherie in 1797 included several minerals containing magnesium, and at the present day it is used by French writers for meerschaum . The mineral has also been called baudisserite from the locality Baudissero near Ivrea in Piedmont . Breunnerite is a ferriferous variety . Magnesite is a product of alteration of magnesium silicates, and occurs as veins and patches in serpentine, talc-schist or dolomite-rock .

It is extensively

mined in the island of Euboea in the Grecian Archipelago, near Salem in Madras, and in California, U.S.A . It is principally used for the manufacture of highly refractory fire-bricks for lining steel furnaces and electric furnaces; also for making plaster, tiles and artificial stone; for the preparation of magnesium salts (Epsom salts, &c.); for whitening paper-pulp and wool; and as a paint .