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An orange-red crystalline substance, C15H10O5, obtained from the buckthorn, rhubarb, etc., and regarded as a derivative of anthraquinone; -- so called from a species of rhubarb (Rheum emodei).

ted to each other as a right-handed to a left-handed glove; -- said of certain hemihedral crystals.

An iron-black mineral of metallic luster, occurring in small orthorhombic crystals, also massive. It contains sulphur, arsenic, copper, and often silver.

A crystal of one species inclosed within one of another, as one of rutile inclosed in quartz.

Having water within; containing fluid drops; -- said of certain crystals.

A mineral of the pyroxene group, orthorhombic in crystallization; often fibrous and massive; color grayish white or greenish. It is a silicate of magnesia with some iron. Bronzite is a ferriferous variety.

llowish green (pistachio) color, occurring granular, massive, columnar, and in monoclinic crystals. It is a silicate of alumina, lime, and oxide of iron, or manganese.

Foreign; unnatural; unusual; -- said of forms of crystals not natural to the substances in which they are found.

A crystallized, transparent mineral of the Zeolite family. It is a hydrous silicate of alumina and lime.

A genus of vascular, cryptogamic, herbaceous plants; -- also called horsetails.

A colorless crystalline substance, C20H22O10, extracted from certain lichens, as the various species of Rocella. It is a derivative of orsellinic acid. So called because of certain red compounds derived from it. Called also erythric acid.

A colorless crystalline substance, C4H6.(OH)4, of a sweet, cooling taste, extracted from certain lichens, and obtained by the decomposition of erythrin; -- called also erythrol, erythroglucin, erythromannite, pseudorcin, cobalt bloom, and under the name phycite obtained from the alga Protococcus vulgaris. It is a tetra…

A crystalline substance obtained from diseased bile, which becomes blood-red when acted on by nitric acid or ammonia.

A white crystalline alkaloid, extracted from sassy bark (Erythrophleum Guineense).

n in ink from an etched plate. Etching figures (Min.), markings produced on the face of a crystal by the action of an appropriate solvent. They have usually a definite form, and are important as revealing the molecular structure. -- Etching needle, a sharp-pointed steel instrument with which lines are drawn in the gro…

A white, crystalline hydrocarbon, regarded as a polymeric variety of ethylene, obtained in heavy oil of wine, the residue left after making ether; -- formerly called also concrete oil of wine.

An unfermentable sugar, obtained as an uncrystallizable sirup by the decomposition of melitose; also obtained from a Tasmanian eucalyptus, -- whence its name.

ving a fine color. Euchroic acid (Chem.), an organic, imide acid, obtained as a colorless crystalline substance, C12H4N2O8 by heating an ammonium salt of mellitic acid. By reduction it is changed to a dark blue substance (euchrone), -- hence its name.

A mineral occurring in transparent emerald green crystals. It is hydrous arseniate of copper.

A brittle gem occurring in light green, transparent crystals, affording a brilliant clinodiagonal cleavage. It is a silicate of alumina and glucina.