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Pollucite: Silica 47%, Alumina 16%. Caesium Oxide 31.4%, Soda 2 8%- An isometric mineral occurring with castor in the granite of the Isle of Elba. It is colorless and
transparent; sometimes dull and gum-like externally. Named after
Pollux of heathen mythology.
Polybasite: Sulphide
of Antimony and Silver. Sulphur 15%, Antimony 9.4%, Silver 75.6%.
Occurs in six-sided tabular prisms with beveled edges. Color
iron-black, but in thin splinters, cherry-red. This mineral was
formerly an important ore of Silver in the "Comstock Lode" of Nevada.
It is at present mined with other silver ores at Ouray, Colorado; in
Montana, Mexico and at many places in Chile. The name is from the
Greek word meaning "many," in allusions to the many bases contained in
this mineral.
Polycrase: A
niobate and titanate of Yttrium, Erbium, Cerium and Uranium. Occurs in
long crystals in Sweden and Norway; and in well-formed prismatic
crystals
in the gold washings in North Carolina. Color black and brownish.
Polydymite: Nickel
Sulphide. Sulphur 40%, Nickel 60%. Occurs in isometric crystals; in
octahedrons; frequently in polysynthetic twins; and often tabular. Color
light-gray to steel-gray, and tarnishes easily. It occurs at Sudbury,
Ontario.
Polyhalite: Hydrous
Sulphate of Calcium, Magnesium and Potassium. Sulphur Trioxide 53.2%,
Lime 18.6%, Magnesia, 6.6%, Potash 15.6%. Occurs usually in compact
or lamellar masses. Color flesh-red or brick-red, sometimes yellowish.
Taste bitter and stringent. It is found in the mines in Austria with
Halite, Gypsum and Anhydrite.
Porpihyry: A
rock consisting of a compact feldspathic base through which crystals of
feldspar are disseminated. There are red, green, and purple varieties
which are highly esteemed
as marbles, and are used as building stones.
Prehnite: An
Acid Orthosilicate. A pale-green mineral with a vitreous luster,
occurring nearly always in crystals, though it occurs also in
stalactitic and granular massive forms. This mineral was named after
Colonel Prehn, who discovered it at the Cape of Good Hope. It is
abundant in copper veins along the north shore of Lake Superior; also
in Connecticut and New Jersey.
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Fifty-five
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