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rring in small masses, or in monoclinic crystals; blue spar. It is a hydrous phosphate of alumina and magnesia.

g a glassy fracture, occurring in translucent trapezohedral crystals. It is a silicate of alumina and potash. It is found in the volcanic rocks of Italy, especially at Vesuvius.

coal, and partly the result of vegetable decomposition; honeystone. It is a mellitate of alumina.

ccuring in delicate groups of crystals, also fibrous massive. It is a hydrous silicate of alumina, lime, and soda.

rystals, and in masses which often have a radiated structure. It is a hydrous silicate of alumina and soda.

ing quartz, occurring with castor or castorite on the island of Elba. It is a silicate of alumina and cæsia. Called also pollux.

dal or mammillary structure, and rarely in distinct crystals. It is a hydrous silicate of alumina and lime.

white or greenish color and pearly luster, consisting chiefly of the hydrous silicate of alumina.

alite, coccolite, augite, etc. They are all silicates of lime and magnesia with sometimes alumina and iron. Pyroxene is an essential constituent of many rocks, especially basic igneous rocks, as basalt, gabbro, etc.

A fluoride of alumina and soda occurring with the Greenland cryolite in octahedral crystals.

een color and micaceous structure, belonging to the chlorite group; a hydrous silicate of alumina, magnesia, and iron; -- called also clinochlore.

Native alumina or aluminium sesquioxide, Al2O3; corundum; esp., the blue transparent variety of corundum, highly prized as a gem. of rubies, sapphires, and of pearlés white. Chaucer.

taining three atoms of oxygen with two atoms (or radicals) of some other substance; thus, alumina, Al2O3 is a sesquioxide.

e name. -- Aluminous slate, or Alum slate (Min.), a kind of slate containing sulphate of alumina, -- used in the manufacture of alum. -- Bituminous slate (Min.), a soft species of sectile clay slate, impregnated with bitumen. -- Hornblende slate (Min.), a slaty rock, consisting essentially of hornblende and feldspar…

A hydrous silicate of alumina, of a greenish color, which, in certain states of humidity, appears transparent and almost gelatinous.

nate, under Sodium. -- Soda alum (Min.), a mineral consisting of the hydrous sulphate of alumina and soda. -- Soda ash, crude sodium carbonate; -- so called because formerly obtained from the ashes of sea plants and certain other plants, as saltwort (Salsola). See under Sodium. -- Soda fountain, an apparatus for dra…

blue or gray color, occuring commonly in dodecahedrons, also massive. It is a silicate of alumina and soda with some chlorine.

e, brown, and black, the red variety being the gem spinel ruby. It consist essentially of alumina and magnesia, but commonly contains iron and sometimes also chromium.

A common mineral of the zeolite family, a hydrous silicate of alumina and lime, usually occurring in sheaflike aggregations of crystals, also in radiated masses. It is of a white or yellowish color, with pearly luster on the cleavage surface. Called also desmine.

lates, also in velvety bronze-colored incrustations. It is a hydrous silicate of iron and alumina.