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Pure silica, like quartz, but crystallizing in hexagonal tables. It is found in trachyte and similar rocks.

tained by powdering lapis lazuli, but now produced in large quantities by fusing together silica, alumina, soda, and sulphur, thus forming a glass, colored blue by the sodium polysulphides made in the fusion. Also used adjectively. Green ultramarine, a green pigment obtained as a first product in the manufacture of ult…

A group of minerals having, a micaceous structure. They are hydrous silicates, derived generally from the alteration of some kind of mica. So called because the scales, when heated, open out into wormlike forms.

als, and also massive, of a brown to green color, rarely sulphur yellow and blue. It is a silicate of alumina and lime with some iron magnesia, and is common at Vesuvius. Also called idocrase.

f manganese, or mixture of different oxides and water, with some oxide of iron, and often silica, alumina, lime, or baryta; black ocher. There are several varieties.

A silicate of zinc, usually occurring massive and of a greenish yellow color, also in reddish crystals (troostite) containing manganese.

A silicate of lime of a white to gray, red, or yellow color, occurring generally in cleavable masses, rarely in tabular crystals; tabular spar.

or making edge tools; Indian steel. It has in combination a minute portion of alumina and silica.

A silicate of iron and lime occurring in black prismatic crystals; -- also called ilvaite. [Spelt also jenite.]

t contains no potash. The name is often loosely applied to mixtures of zaffer proper with silica, or oxides of iron, manganese, etc. [Written also zaffre, and formerly zaffree, zaffar, zaffir.]

A term now used to designate any one of a family of minerals, hydrous silicates of alumina, with lime, soda, potash, or rarely baryta. Here are included natrolite, stilbite, analcime, chabazite, thomsonite, heulandite, and others. These species occur of secondary origin in the cavities of amygdaloid, basalt, and lava,…

ineral occurring in tetragonal crystals, usually of a brown or gray color. It consists of silica and zirconia. A red variety, used as a gem, is called hyacinth. Colorless, pale-yellow or smoky- brown varieties from Ceylon are called jargon. Zircon syenite, a coarse-grained syenite containing zircon crystals and often a…

h mineral occurring in orthorhombic, prismatic crystals, also in columnar masses. It is a silicate of alumina and lime, and is allied to epidote.

A fluosilicate of alumina occurring in tetrahedral crystals at the Zuñi mine in Colorado.