Bulletin, Issue 2

Front Cover
Virginia Geological Survey, 1906 - Geology
 

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Page 71 - TENSILE STRENGTH.—The tensile strength of a clay is the resistance which it offers to rupture on being pulled apart when airdried. It is an important property by virtue of which the unburned clay ware is able to withstand shocks and strains of handling and probable shrinkage in drying. Through it, also, the clay
Page 79 - feldspar, Norwegian quartz, Carrara marble, and pure ferric oxide. Cone No. 1 melts at the same temperature as an alloy composed of one .part of platinum and nine parts of gold, or at 1150C. (2102F.). Cone 20 melts at the highest temperature obtained in a porcelain furnace, or at
Page 60 - is found in many clays, and in the low-grade ones may be present in large quantities at times. Quite a large number of minerals may serve as sources of lime in clays, but all fall into one of the three following groups: 1. Carbonates. Calcite, dolomite. 2. Silicates containing lime, such as feldspar, garnet.
Page 60 - or if silica is present. A low iron content is, therefore, desirable in refractory clays, and the average of a number of analyses of these shows it to be 1.3 per cent. Brick clays which are usually easily fusible, contain from 3 to 7 per cent. of iron oxide. Effect of Iron Oxide on Absorptive Power and Shrinkage of
Page 36 - most terrace clays are rather sandy, with here and there pockets of fine, plastic clay. They also frequently contain more or less organic matter. Along its inner edge the terrace may be covered by a mixture of clay, sand and stones, washed down from neighboring slopes.
Page 57 - OF IRON OXIDE IN CLAYS.—Iron oxide is one of the commonest ingredients of clay, and a number of different mineral species may serve as sources of it, the most important of which are grouped below: Hydrous oxide, limonite; oxides, hematite, magnetite; silicates, biotite, glauconite (greensand), hornblende, garnet;
Page 109 - process.—In this method of molding the clay is tempered with less water, and is consequently much stiffer. The principle of the process consists in taking the clay thus prepared and forcing it through a rectangular die in the form of a bar which is then cut up into bricks. The machine now most used is known as the auger type.
Page 65 - We, therefore, see that the minerals supplying alkalies are all silicates of complex composition. Each has its fixed melting point, and the temperature at which the alkalies flux with the clay will depend on the containing mineral, and also on the size of the grains. If the alkali-bearing mineral grains decompose, the potash or soda
Page 37 - covered by a bed of sandy clay (b). Beds of clay and shale sometimes show folds or undulations. In the Coastal Plain clays of Virginia these are rarely seen, but in the shales of the Appalachian region they are by no means uncommon. Where beds of clay or shale are bent into arches (anticlinal
Page 30 - rock — the change from the rock t'o clay being, therefore, a sudden one, and not due to a gradual breaking down of the minerals in the rock, as in the case of granite. FIG. 1. Section showing

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