. The elements of geology, for popular use : containing a description of the geological formations and mineral resources of the United States. Geology; Geology. 40 FELDSPAR. MiCA, and forms a constituent part of numerous rocks. It is not as hard as quartz, but more brittle. It is composed of thin laminae or plates, which are most commonly four or six sided prisms, which have a bright, pearly lustre, which distinguishes it from quartz, whose lustre is dull. Fig. An oblique parallelopiped, the primi- tive form of feldspar. The colours of feldspar are white, gray, miik- while, yellowish or re
. The elements of geology, for popular use : containing a description of the geological formations and mineral resources of the United States. Geology; Geology. 40 FELDSPAR. MiCA, and forms a constituent part of numerous rocks. It is not as hard as quartz, but more brittle. It is composed of thin laminae or plates, which are most commonly four or six sided prisms, which have a bright, pearly lustre, which distinguishes it from quartz, whose lustre is dull. Fig. An oblique parallelopiped, the primi- tive form of feldspar. The colours of feldspar are white, gray, miik- while, yellowish or reddish white, sometimes in- clining to green. When crystallized it is translu- cent. It maybe melted into a glass without adding any alkali, because an alkali forms one of its con- stituent ingredients. It is found, on analysis, to contain silex 63; alumine 17; potash 13; lime 3; oxide of iron 1: it is probably owing to the fact that feldspar contains potash that it is so easily decom- posed, although nearly as hard as quartz. Those feldspars which do not decay on exposure to the atmosphere contain but little, if any, potash. When decomposed it forms a kind of clay called kaolin, from which china or porcelain-ware is made by burning. In its manufacture a little lime is added as a, flux, which tends to soften it in the fire, and, on cooling, it assumes the requisite degree of hard- ness. Feldspar forms a constituent part of granite, gneiss, and mica slate, and enters more or less into the formation of greenstone and most volcanic sub- stances, as well as porphyry and sienite. In some parts of the world it forms entire mountains; as in Siberia, Scotland, Labrador, &c. Mica* sometimes called isinglass, is also compo- sed of silex, alumine, potash, and oxide of iron. * From the Latin micans, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may no
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1846
