classification...rocks whose sand grains consist of at least 95 percent quartz. If the sand grains consist of more than 25 percent feldspar (and feldspar grains are in excess of rock fragments), the rock is termed arkosic arenite or “arkose,” although such sandstones are also somewhat loosely referred to as feldspathic sandstones. In subarkosic arenite (or subarkose), feldspar sand grains likewise...
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