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Show :(i , I 1l!> a a Crawford and Burenek: Economic Minerals 29. 30. 113 "Soda Microline", varies from "string perthite" to incipient gridiron twinninq, sometimes with wavy extinction micro mosaics and frequently replacing anorthoclase. Microperthite. This appears to be the equivalent of H. L. Alling's class 4 perthite (beta-alpha perthite ) caused by the loss in solubility during change in modification from orthoclase-albite to microcline-analbite. However, since this is regarded as the result of hydrothermal replacement it might be his type 3 or 10. It appears paraqenetically between "soda microcline" (#29) and albite (#31). 31. 32. Albite, the well twinned "patch" variety?", often well devel oped around tourmaline and beryl after microperthite (of #39) and before the well developed microcline, with beau tiful gridiron twinning, which replaces it. Microline, pink massive feldspar, the chief commercial prod uct of the mine; beautiful gridiron twinning well developed and replacement textures clear cut and extensive. .... 33. Perthite, typical microcline with vein-type albite inclusions, has a paler pink than #32, probably due to the prevalence of the albite bands. The gridiron twinning is coarser than in #32 and perthite of this type was found replacing the microcline of #32 with which it is intimately associated and with which it makes up the masses of shipping grade feld . .... spar. 34. Muscovite, hydrothermal; occurring in clear sheets; it is not yet certain whether it is this or the pneumatolytic muscovite that makes up most of the shipping mica. The latter is be lieved to be the older muscovite of #15; since under the microscope the older muscovite is freer from inclusions and seems to be more perfect where it is. not too corroded or replaced by later minerals. This #34 more typically forms skeletal crystals with many microcline and other mineral residuals. 35. Albite, vein lets with quartz .. It may be the same generation of albite as that in the perthite of #33. 36. Vein quartz cutting all other older minerals. 37. Kaolinite (?). This may be nacrite. It is present in vein lets and intersticial cavities in corroded beryl. Mineals of Economic Significance FELDSPAR: There are two chief potash feldspars, orthoclase and microcline. Both have the same formula which 'is 6Si02• In pegmatites, microcline is far more abundant K20.A1203• and in this "Allinq, H. L., Perthites: Am. Mineralogist, Vol. 17, p. 61. . |
