Small quartz overgrowths are fairly common in some specimens, although in no case are they pronounced or well developed. In summary, most grains have the internal characteristics of igneous (plutonic) quartz (Krynine, 1946). Large fluid inclusions are also somewhat rare. A very few grains contain carbonaceous inclusions. Apatite is particularly common, and the following minerals were also identified: rutile, biotite, hornblende, tourmaline, and chlorite. Bubble planes form the most common type, but several varieties of idiomorphic and allotriomorphic crystalline inclusions also are observed. Many types of inclusions are observed, indicating several modes of origin. Flamboyant extinction typical of some vein quartz is extremely rare. Nearly all the large rounded quartz grains show strain shadows. Relatively straight extinction in most of the grains indicates that they are nearly strain-free, but from 5 to 35 percent show undulose extinction. The sorting of quartz in those samples which contain the large rounded grains is seemingly bimodal. In general the quartz (and feldspar) grains themselves are rather well sorted but they are commonly associated with clay minerals. The larger rounded grains are approximately 0.2 to 1.0 mm in diameter and are most abundant in the upper part of the section (Whitehorse, Taloga formations), although they are found as low as the upper Salt Plain formation. Nearly all the quartz grains throughout the section are of silt size or very fine-grained sand size (less than 125 microns in diameter). Much of the frosted appearance seems to be produced by small quartz overgrowths. Some of the large well-rounded grains have frosted surfaces. Some grains are slightly etched and are partly replaced by carbonates or clay minerals. The surfaces of some grains are polished and have an orange color. The degree of rounding, as will be shown in the section on petrography, seemingly is not entirely a function of differences in particle size. Most of the grains are subangular, except for the scattered large grains in the upper part of the section, which are almost invariably very well rounded. The quartz grains of sand and coarse silt size show a wide range in roundness from extremely angular (particularly in the finer sizes) to very well rounded.
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