144 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
and must be carefully separated from feldspar which is to be used for pottery purposes. The colored varieties occasionally are found also in the solid pegmatite, as at the Newry mine (p. 76), but where occurring in this way seldom yield much "gem material" because of the difficulty of removing them unfractured from their matrix. The colored tourmalines showing the greatest perfection in crystal form and yielding most of the gem stock occur in pockets in the coarse pegmatite bodies. For a detailed description of their mode of occurrence the reader is referred to the description of Mount Mica (pp. 81-93).
Outside of Maine gem tourmalines are produced in the United States in important amounts only in Connecticut and California. Abroad they are found in Brazil, in the Ural Mountains, and in Ceylon.
Mining, prices, etc.—Mount Mica in Paris and Mount Apatite in Auburn are the only localities where systematic mining for tourmalines is now being carried on, although a few gem tourmalines are occasionally found at certain of the feldspar quarries. The quarries have been described in the detailed locality descriptions. In general, the excavation must proceed with great caution; the drilling must be done in a most careful manner, much of it by hand; and heavy charges of explosives must be avoided because of the liability of shattering valuable gem material.
Most of the gem tourmalines now mined in Maine, when not preserved for museum purposes, are cut within the State by lapidaries whose workmanship is said often to equal that of the best New York cutters. The size and general character of the finest gems which have been cut is described in the discussion of Mount Mica. The great bulk of the cut tourmalines marketed are, however, below 3 carats in size. Rubellites and stones of a color approaching an emerald green are the most valuable.
The prices obtained in Maine are higher than those current in New York City, because most are sold at retail to residents of the State or to summer tourists and have an enhanced value as souvenirs. Rubellites and emerald-green varieties bring at retail from $8 to $20 per carat. The indicolite and olive-green varieties bring from $6 to $18 a carat.
BERYL.
CHEMICAL AND PHYSICAL PROPERTIES.
Under the name beryl are included the opaque beryl found in nearly all the pegmatite dikes and the much rarer gem varieties, emerald, aquamarine, golden beryl, and caesium beryl. In chemical composition beryl is a silicate of beryllium and alumina having the general formula of Be3Al2Si6018 or 3BeO.Al203.6Si02, but with the beryllium oxide replaced in some varieties by soda, lithia, or calcium oxide. The mineral has a hardness of 7-1/2 to 8; that is, it can not
Flickr
Stumbleupon
Scribd
