Manual of Mineralogy Containing an Account of Simple Minerals and Also a Description and Arrangement of Mountain Rocks (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated.1821 Excerpt: ... to the atmosphere; but the quartz is never altered. Granite, with earthy felspar, is found in Cornwall 6. Crystallization of Hie Constituent Parts.--Sometimes the constituent parts of granite are regularly crystallized; principally, however, the felspar and quartz. The mica sometimes occurs in nests, unmixed with the other constituent parts, and these have been confounded with fragment. Sometimes the constituent parts are so arranged, that when the specimen is cut, its surface bears a resemblance to written characters: hence this variety has been denominated Graphic Stone, and is the Pegmatite of some geologists. This particular variety is found at Portsoy, Island of Harris, and in the Island of Arran . Granite, with regularly crystallized felspar, occurs in the Island of Arran, in many places on the Continent of Europe, and also in South America. At Mosmt St Gothard, all the three constituent parts are found crystallized together. In the Island of Arran and in the Saxon Erzgebirge, there is a remarkable variety of granite, in which the felspar, quartz, and mica, have a diverging radiated structure, 7. Imbedded and Venigeaous Minerals.--Besides felspar, quartz, and mica, the essential constituent parts of granite, and those minerals that tak$ the place of the mica, viz. hornblende and chlorite, others sometimes occur in it. These are schorl, garnet, and tinstone. The following also occasionally occur either imbedded in the rock, or ijj veins that traverse it, viz. rock-crystal, adularia, chlorite, pinite, actynolite, common opal, topaz, corundum, fluor-spar, beryl, diallage, epidote, apatite, magnetical iron-ore, and iron-pyrites. 8. Structure.--Granite, besides the granular, exhibits various other kinds of structure, such as porphyritic, globular, tabular, ..