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powder, slow-burning gunpowder, in large cubical grains. -- Scotch pebble, varieties of quartz, as agate, chalcedony, etc., obtained from cavities in amygdaloid.

Powdered fledspar, kaolin, or quartz, used in the manufacture of porcelain.

gem. It is a silicate of glucina, and receives its name from its deceptive similarity to quartz.

A variety of quartz, of a color between grass green and leek green, which is found associated with common chalcedony. It was much esteemed by the ancients for making engraved ornaments.

Manganese dioxide, occurring in tetragonal crystals nearly as hard as quartz.

A colorless transparent mineral, resembling quartz, occurring with castor or castorite on the island of Elba. It is a silicate of alumina and cæsia. Called also pollux.

g, porphyry, that is, characterized by the presence of distinct crystals, as of feldspar, quartz, or augite, in a relatively fine-grained base, often aphanitic or cryptocrystalline.

ng of a fine-grained base (usually feldspathic) through which crystals, as of feldspar or quartz, are disseminated. There are red, purple, and green varieties, which are highly esteemed as marbles. Porphyry shell (Zoöl.), a handsome marine gastropod shell (Oliva porphyria), having a dark red or brown polished surface,…

for the ordinary ray, and the former is refracted nearer to the axis than the latter, as quartz and ice; -- opposed to negative crystal, or one in which this characteristic is reversed, as Iceland spar, tourmaline, etc. -- Positive degree (Gram.), that state of an adjective or adverb which denotes simple quality, wit…

A pseudomorphous crystal, as a crystal consisting of quartz, but having the cubic form of fluor spar, the fluor crystal having been changed to quartz by a process of substitution.

A large vein of auriferous quartz; -- so called in Australia. Hence, any body of rock yielding valuable ore. Reef builder (Zoöl.), any stony coral which contributes material to the formation of coral reefs. -- Reef heron (Zoöl.), any heron of the genus Demigretta; as, the blue reef heron (D.jugularis) of Australia.…

those of the isometric system. A uniaxial crystal is said to be optically positive (like quartz), or optically negative (like calcite), or to have positive, or negative, double refraction, according as the optic axis is the axis of least or greatest elasticity for light; a biaxial crystal is similarly designated when…

A quartzose trachyte, an igneous rock often showing a fluidal structure. -- Rhy`o*lit"ic, a.

ss kind found on rocks, as Arabis petræa, A. lyrata, etc. -- Rock crystal (Min.), limpid quartz. See Quartz, and under Crystal. -- Rock dove (Zoöl.), the rock pigeon; -- called also rock doo. -- Rock drill, an implement for drilling holes in rock; esp., a machine impelled by steam or compressed air, for drilling hol…

Acicular rutile occurring in reticulated forms imbedded in quartz.

Resembling sagenite; -- applied to quartz when containing acicular crystals of other minerals, most commonly rutile, also tourmaline, actinolite, and the like.

made of sand more or less firmly united. Common or siliceous sandstone consists mainly of quartz sand.

r slates. The common kinds are mica schist, and hornblendic schist, consisting chiefly of quartz with mica or hornblende and often feldspar.

An indigo-blue variety of quartz.

r as a dark crystalline substance with a meetallic luster. Its oxide is silica, or common quartz, and in this form, or as silicates, it is, next to oxygen, the most abundant element of the earth's crust. Silicon is characteristically the element of the mineral kingdom, as carbon is of the organic world. Symbol Si. Atom…