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352 Glossary
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Phosphorescence. The property possessed by substances of emitting light in certain conditions.
Pigeon Blood. A deep clear red; the gem colour of the most highly prized specimens of the ruby.
Placer. A deposit of gem minerals found separately, sometimes as rolled pebbles, in alluvium or diluvium, or beds of streams.
Play of Colours. (See colour-play.)
Pleochrism. The term applied to minerals in which a different shade of colour is seen in more than two directions.
Polarisation. In optics, a state into which the ethereal undulations which cause the sensation of light are brought under certain conditions.
Pomegranate. Translation of the Hindu name for spinel.
Precious. (See " Noble.")
Primary Situation. A mineral found in the rock in which it was formed.
Prism. (Geometry.)
A solid having similar and parallel bases, its sides forming similar
parallelograms. (Optics.) Any transparent medium comprised between
plane faces, usually inclined to each other.
Prospecting. Searching for gem fields or mines.
Pulsator. (See Jig; Jigger.)
Pyroelectric. (Thermo-electric.) Pertaining or relating to electric currents or effects produced by heat.
Quality. Native values of a gem irrespective of colour and cut.
Reconstructed. A
term applied to an artificial gem composed of fused particles of a
natural precious stone—" Reconstructed rubies " although not difficult
to differentiate by tests, from the red corundum of gem quality from
Nature's laboratory, attain some commercial success. Also called "
Scientific Ruby."
Reflection. The act of reflecting or throwing back, as of rays of light.
Refraction. Bending back. In optics, the refraction of a ray of light into a number of other rays forming a
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