Returned to my collecting area with a rock that showed interesting character but little lime/green under SW UV. Best to break it open to see if any more UV would be revealed. While I hoped for decent response, I was not expecting this rhyolite to be a geode.
Last year I collected a similar looking rock from the Armagosa Valley in Nye County, Nevada. Bryan Smalley cut it open and it was just a sad looking mix of brown rhyolite and quartz. This is now my first self-collected geode. I normally would not hunt them since I have no idea where they might be.
I am still looking for uranium occurrences and have had yet to find any. I may, though, have identified sanidine crystals in tuff so that is a good thing. I’ll be back.
Breaking it Open In The Field
Under SW UV, Along With My First Brachiopod (Shell)
I also found my first brachiopod! Photo below:
I may have also discovered a concretion naturally split apart. See below.
Concretions are typically sandstone based. Those might form around a piece of a shell (limestone in nature) or a bit of calcite. My rock fizzes hardly at all, which makes me think it is not sedimentary. Bates and Jackson say concretions can also form around a leaf, bone or fossil and that concretions can derive from “fragmental volcanic rocks.” I’m still reading up on this.
Picture below is my rock and a reference sample I have from Geological Specimen Supply. That rock comes from the Tule Wash in Imperial, County, California.
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