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A crystalline rock consisting of quarts and mica, common in the tin regions of Cornwall and Saxony.

rd. -- Ground mass (Geol.), the fine-grained or glassy base of a rock, in which distinct crystals of its constituents are embedded. -- Ground parrakeet (Zoöl.), one of several Australian parrakeets, of the genera Callipsittacus and Geopsittacus, which live mainly upon the ground. -- Ground pearl (Zoöl.), an insect o…

A crystalline substance (C5H5N5O) contained in guano. It is also a constituent of the liver, pancreas, and other glands in mammals.

e of lime (calcium). When calcined, it forms plaster of Paris. Selenite is a transparent, crystalline variety; alabaster, a fine, white, massive variety.

The coloring principle of logwood. It is obtained as a yellow crystalline substance, C16H14O6, with a sweetish taste. Formerly called also hematin.

ored, 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.

An instrument for measuring the forms and angles of salts and crystals; a goniometer.

ying harmaline (in the Peganum harmala), and obtained from it by oxidation. It is a white crystalline substance.

A hydrous silicate of alumina and baryta, occurring usually in white cruciform crystals; cross-stone.

substance found in the root of the elecampane (Inula helenium), and extracted as a white crystalline or oily material, with a slightly bitter taste.

A glucoside obtained as a white crystalline substance by partial oxidation of salicin, from a willow (Salix Helix of Linnæus.)

ucoside accompanying helleborin in several species of hellebore, and extracted as a white crystalline substance with a bittersweet taste. It has a strong action on the heart, resembling digitalin.

A poisonous glucoside found in several species of hellebore, and extracted as a white crystalline substance with a sharp tingling taste. It possesses the essential virtues of the plant; -- called also elleborin.

A reddish brown or violet crystalline substance, C16H12O6, got from hematoxylin by partial oxidation, and regarded as analogous to the phthaleins.

de, so called because of the red color of the powder. It occurs in splendent rhombohedral crystals, and in massive and earthy forms; -- the last called red ocher. Called also specular iron, oligist iron, rhombohedral iron ore, and bloodstone. See Brown hematite, under Brown.

A crystalline or amorphous pigment, free from iron, formed from hematin in old blood stains, and in old hemorrhages in the body. It resembles bilirubin. When present in the corpora lutea it is called hæmolutein.

Having half of the similar parts of a crystals, instead of all; consisting of half the planes which full symmetry would require, as when a cube has planes only on half of its eight solid angles, or one plane out of a pair on each of its edges; or as in the case of a tetrahedron, which is hemihedral to an octahedron, it…

The property of crystallizing hemihedrally.

Having the two ends modified with unlike planes; -- said of a crystal.

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.