Specimen: 2013-001

This sample is a plutonic rock dominated by mostly anhedral feldspar and a lesser amount of quartz. The crystalline structure is generally coarse. Maximum crystal dimension is 15 mm (feldspar) and minimum is .1 mm (quartz). Modal grain size is from 4 to 1.5 mm. There are a variety of feldspar twinning patterns including tartan (microcline), Carlsbad, and albite. Grain boundaries range from smooth curving to substantially consertal sutured. The latter is particularly common among quartz and feldspar grain boundaries. Intergrowth textures include microperthitic involving multiple species of feldspar and granophyric with plagioclase intergrown with quartz. Accessory minerals include biotite, which is common at about 10 percent of slide area, and muscovite, which is extremely rare. No amphiboles or pyroxenes are visible in this slide. Opaques are also relatively rare and comprise less than 5 percent of slide area. There are slight signs of insipient weathering of feldspars with many grains presenting a dusty look. What is likely sericite is present in small patches (~10 µm) on some feldspar grains. Rarely, grain boundaries and cracks in grains have begun to fill with reddish brown clay material (>20 µm in width).
7/7/2015 MP