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Show Utah Academy of Sciences, Arts and Letters 114 can be respect the Grover Pegmatite is no exception. Microcline identified under, the microscope by its double-polysyn thetic or "gridiron" twinning. In the Grover Pegmatite great Some quantities of this mineral occur in relatively pure masses. of them have crystal continuity over several feet and mayor may not have appreciable quantities of quartz and/or albite intergrown. When the intergrowths in the microcline are albite and occur in visible lamallae the intergrowth is called perthite. The same type of intergrowth on a microscopic scale is called microperthite. Both types make a satisfactory commercial feldspar. Often an intergrowth with quartz occurs in which the quartz also is skeletal in nature and wide areas are in crystal continuity. Such inter growths frequently take on the appearance of cuniform charac ters and, hence, have been given the name of "graphic granite." With a large predominance of the quartz constituent the graphic economic worth. granite gives way to "bull" quartz of little or no There are considerable masses of this material in the Grover Pegmatite, which at present are worthless, but which with im proved roads and mechanization might eventually find use, at a price that would pay for the freight, should the glass industry become important at Denver. It has to be mined in order to the feldspar. Anorthoclase, and soda-microcline, two recover occur in the minor feldspar complex at the Grover readily feldspars, Pegmatite. They can be recognized only by microscopic study However, since both of them are, like the in polarized light. or combinations of the potash and soda mixtures either perthites, feldspar molecules, their intergrowth with the other commercial potash feldspars creates no special problem. In general the potash feldspar zone of commercial grade been occurs above the mica-beryl-albite zone and appears to have formed in part as a by-product of the pneumatolytic action that produced the mica-beryl-albite zone below. Whether the solu tions rich in by-product silica and potassia moved upward only or a few feet before replacing the adjacent portions of the dike, whether they moved laterally eastward and upward for an in definite distance following along the "roof" of the zone created by the lpreceding hotter pneumatolytic emanations is not clear from the preliminary study. The determination of this point might have an important bearing on the probable depth and extent of the deposit. MUSCOVITE: covite mica have As previously noted, sixty-eight tons of mus already been mined from' the Grover Pegmatite. .. This represents 2.1 0% of the total tonnage taken from the pit. Some of the mica is in crystals, or "books," eighteen inches across. Unfortunately, much of this is "ruled," contains iron impurities, and is otherwise defective as "sheet" mica, and must be marketed With careful sorting some mica might be recovered for as scrap. |
