Monday, May 12, 2014

Geo 730: May 12, Day 498: Sheared Granite

This is a countertop in the hotel we stayed at in Coos Bay, a Super 8, after visiting Shore Acres and Sunset Bay State Parks on March 8, 2012. At a rough visual estimate, and taking the pinkish/buff minerals as alkali feldspar, the whiter/creamy minerals as plagioclase, and the darker grey as quartz, I'm putting the akali feldspar at ~25%, plag at ~40%, quartz at ~30%, with the remaining 5% or less as mafic minerals, probably mostly amphibole and magnetite. According to this QAP diagram (scroll down a bit past the rock photos and following block of text), that makes it a true granite, assuming I've got the mode more or less right. The interesting things here are that, first, the rock appears to have a distinct metamorphic fabric, with the mineral grains flattened roughly parallel to horizontal in this view, and second, there is a distinct right-lateral shear zone running vertically on the right side. I appreciate when nice rocks are used in the design of a living space, even if I only live there overnight.

Photo unmodified. March 9, 2012. FlashEarth location.

1 comment:

Shereena Dyer said...

I would have to get a closer look, but it looks like there is some biotite in there as well. This reminds me of the countertops I had in the place I rented when I lived in Las Vegas. I believe the industry name for the granite that was installed in my place is Santa Clara "Granite", except my counters had coarse grains of what I think was garnet. Did not make much sense to me.