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silicate of lead and potassium. It is used for tableware, and for optical instruments, as prisms, its density giving a high degree of dispersive power; -- so called, because formerly the silica was obtained from pulverized flints. Called also crystal glass. Cf. Glass.

A mineral occurring in greenish gray six-sided prisms, having a greasy luster. It is probably a pseudomorph after elæolite.

A hydrous oxide of iron, occurring in prismatic crystals, also massive, with a fibrous, reniform, or stalactitic structure. The color varies from yellowish to blackish brown.

A luminous circle, usually prismatically colored, round the sun or moon, and supposed to be caused by the refraction of light through crystals of ice in the atmosphere. Connected with halos there are often white bands, crosses, or arches, resulting from the same atmospheric conditions.

A substance, in the form of reddish brown, microscopic, prismatic crystals, formed from dried blood by the action of strong acetic acid and common salt; -- called also Teichmann's crystals. Chemically, it is a hydrochloride of hematin.

A hydrous phosphate of zinc in transparent prismatic crystals.

nsparent variety of calcite, the best of which is obtained in Iceland. It is used for the prisms of the polariscope, because of its strong double refraction. Cf. Calcite.

A silicate of iron and lime occurring in black prismatic crystals and columnar masses.

A kind of deep blue, one of the seven prismatic colors.

Of or pertaining to the iris or rainbow; prismatic; as, the iridal colors. Whewell.

hibition of colors like those of the rainbow; the quality or state of being iridescent; a prismatic play of color; as, the iridescence of mother-of-pearl.

Having colors like the rainbow; exhibiting a play of changeable colors; nacreous; prismatic; as, iridescent glass.

An appearance resembling the rainbow; a prismatic play of colors. Tennyson.

Exhibiting the prismatic colors; irised; iridescent. W. Phillips.

A philosophical toy for exhibiting the prismatic tints by means of thin films.

A variety of mimetite or arseniate of lead in hexagonal prisms of a fine orange yellow. [Written also campylite.]

A mineral consisting of sulphate of lead, occurring either massive or in long slender prisms, of a greenish white or gray color.

Bright; vivid; glowing; strong; vigorous. The colors of the prism are manifestly more full, intense, and lively that those of natural bodies. Sir I. Newton. His faith must be not only living, but lively too. South. Lively stones (Script.), saints, as being quickened by the Spirit, and active in holiness.…

The longer of two diagonals, as of a rhombic prism. See Crystallization.

See Macroprism.