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eral of a grayish or yellowish color, found in Bolton, Massachusetts. It is a silicate of magnesium, belonging to the chrysolite family.

a white or gray color occurring massive and in isometric crystals; in composition it is a magnesium borate with magnesium chloride.

A variety of enstatite, often having a bronzelike luster. It is a silicate of magnesia and iron, of the pyroxene family.

white, pearly mineral, occurring thin and foliated, like talc, and also fibrous; a native magnesium hydrate.

An apple-green mineral, a hydrous arseniate of nickel, cobalt, and magnesia; -- so named from the Sierra Cabrera, Spain.

nding to form, or to become, a calx or earthlike substance on being oxidized or burnt; as magnesium, calcium. etc.

A hydrous chloride of potassium and magnesium, sometimes found associated with deposits of rock salt.

A hydrous silicate of magnesium, allied to serpentine, occurring in waxlike masses of a yellow or greenish color.

ug. -- Drawing chalk. See Crayon, n., 1. -- French chalk, steatite or soapstone, a soft magnesian mineral. -- Red chalk, an indurated clayey ocher containing iron, and used by painters and artificers; reddle.

and micaceous to granular in structure. They are hydrous silicates of alumina, iron, and magnesia. Chlorite slate, a schistose or slaty rock consisting of alumina, iron, and magnesia.

A fluosilicate of magnesia and iron, yellow to red in color, often occurring in granular form in a crystalline limestone.

A mineral, composed of silica, magnesia, and iron, of a yellow to green color. It is common in certain volcanic rocks; -- called also olivine and peridot. Sometimes used as a gem. The name was also early used for yellow varieties of tourmaline and topaz.

own and decomposition, in part, of rocks containing aluminous minerals, as granite. Lime, magnesia, oxide of iron, and other ingredients, are often present as impurities.

A magnesian variety of dolomite.

A supposed alkaloid obtained from croton oil by boiling it with water and magnesia, since found to be merely a magnesia soap of the oil. Watts.

A mineral consisting of the carbonate of lime and magnesia in varying proportions. It occurs in distinct crystals, and in extensive beds as a compact limestone, often crystalline granular, either white or clouded. It includes much of the common white marble. Also called bitter spar.

A similar oxide, having a slight alkaline reaction, as lime, magnesia, strontia, baryta.

lization; often fibrous and massive; color grayish white or greenish. It is a silicate of magnesia with some iron. Bronzite is a ferriferous variety.

Sulphate of magnesia having cathartic qualities; -- originally prepared by boiling down the mineral waters at Epsom, England, -- whence the name; afterwards prepared from sea water; but now from certain minerals, as from siliceous hydrate of magnesia.

Native sulphate of magnesia or Epsom salt.