Tuesday, August 8, 2017

A "Twofer"

An example of an image that serves two purposes...

Differential Weathering and the "universal melding of joy and grief" for field geologists.

This is a scanned 35mm slide from 40+ years ago, somewhere on the Georgia Piedmont (revisiting that past error of not labeling slides).

Prior to eons of Chemical Weathering, (based upon texture observations and a knowledge of prevailing local rock types), this was probably an Amphibolite, with some quartz-rich intervals (including the ledge upon which the Estwing prybar is perched).

"Differential Weathering" is due to the relative difference of susceptibility to Chemical Weathering between Mafic (Fe-rich silicate minerals) vs. Quartz.  Generally speaking, the minerals "higher" on the Bowen Reaction Series (including the Fe-Mg rock-forming minerals, e.g., Pyroxenes, Amphiboles, and Biotite) are more susceptible to chemical weathering at (or near) the surface.  In other words, at a quick glance, the ledges are probably Quartz.

As for the "universal melding of joy and grief", it is reference to finding (and then losing) tools in the field.  It was the subject of a past post, from 2011.  In other words, the post included the regrets of lost hammers, prybars, chisels, handlenses,...and other items.  We usually leave these things because we are tired.  Sometimes we are so obsessed with our newfound "toys" (that we may have carried several hundred yards to the vehicles), that we don't want to make one more trip back to the area to check for tools.

The Estwing prybar in the photo had such an "experience".  I found it at a now long-forgotten locality, kept and used it for a few years, then left it somewhere else.  (The "great circle of life"?)  I hope another Geologist found it and took it home.  So, if you do find a tool in the field, say a little "prayer of empathy" for the fellow scientist that lost it.

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