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An instrument for examining the dichroism of crystals.

Having two of the intersections between the three axes oblique. See Crystallization.

Having two plane faces; as, the dihedral summit of a crystal. Dihedral angle, the angular space contained between planes which intersect. It is measured by the angle made by any two lines at right angles to the two planes.

A red crystalline nitrogenous substance or artificial production, which by reduction passes directly to indigo.

Crystallization in two independent forms of the same chemical compound, as of calcium carbonate as calcite and aragonite.

Crystallizing under two forms fundamentally different, while having the same chemical composition.

A colorless, crystalline hydrocarbon, C20H14, obtained from naphthylene, and consisting of a doubled naphthylene radical.

A crystallized variety of pyroxene, of a clear, grayish green color; mussite.

A hydrous silicate of copper, occurring in emerald-green crystals.

An igneous, crystalline in structure, consisting essentially of a triclinic feldspar and hornblende. It includes part of what was called greenstone.

A white, crystalline, nitrogenous substance obtained by the reduction of isatin. It is a member of the indol series; -- hence its name.

A white crystalline substance, C6H5.C6H5, obtained by leading benzene through a heated iron tube. It consists of two benzene or phenyl radicals united.

A crystalline nitrogenous base, C10H8N2, obtained by the reduction of pyridine.

olored rays, arising from their different refrangibilities. Dispersion of the optic axes (Crystallog.), the separation of the optic axes in biaxial crystals, due to the fact that the axial angle has different values for the different colors of the spectrum.

A white, crystalline, aromatic hydrocarbon, C14H14, consisting of two radicals or residues of toluene.

eeth; -- also called tooth ornament. Dogtooth spar (Min.), a variety of calcite, in acute crystals, resembling the tooth of a dog. See Calcite. -- Dogtooth violet (Bot.), a small, bulbous herb of the Lily family (genus Erythronium). It has two shining flat leaves and commonly one large flower. [Written also dog's-toot…

sting 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 counterfeit gem, composed of two pieces of crystal, with a color them, and thus giving the appearance of a naturally colored gem. Also, a piece of paste or glass covered by a veneer of real stone.

A cavity in a rock, having its interior surface studded with crystals and sometimes filled with water; a geode.

Covered with a large number of minute crystals.