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GLOSSARY.
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Absorption Bands.—The
absorption bands of a substance are dark bands seen in the spectroscope
when the substance is interposed between a source of white light and
the instrument.
Agglomerate.—A rock filling the vent of a volcano and composed of large fragments ejected by the volcano.
Allotriomohphic Minerals.—Minerals with forms other than their own proper form. Duo to pressure of surrounding bodies.
Allotropish.—An
element is allotropic when it occurs in several distinct forms without
change of chemical composition: for instance, red and yellow
phosphorus, or carbon as Graphite and Diamond.
Anhydrous. -Without water.
Aqueous Theory.—A
theory which maintains that all minerals were deposited from a simple
solution, comparable to the deposition of crystals of saltpetre from a
solution in water.
Asterisk.—The property of exhibiting a star-like light.
Basal Plane.—A plane on the termination of a crystal, cutting the principal axis at unit length and lying parallel to the other axes.
Basic Rocks......Rocks containing a low proportion of silica.
Biaxial Cry'stals show
three directions of optical elasticity, and hence have three indices of
refraction. All crystals of the orthorhombic, monosymmetric and
triclinic systems are biaxial. There are two directions in which light
travels with equal velocity.
Botryoidal.—Like a bunch of grapes.
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