Unexpected Geode Find!

January 8th, 2020 Update:

Master agate and geode cutter and polisher Jeffrey Anderson says what I found was a thunderegg, similar to what I bought from Christopher at the Basin Range Volcanics Geolapidary Museum near Deming, New Mexico. Anderson’s comments:

“That geode is what would be generally referred as “thunderegg” and it’s lined with chalcedony and quartz. The “thundereggs” are associated with any rhyolitic deposits. It is common for chalcedony in thundereggs to fluoresce green under shortwave ultraviolet supposedly due to uranium impurities. 🙂 It is a nice find. :)”

Jeffrey Anderson’s store is called Dwarves Earth Treasures. He will be at Quartzsite this year. Here is his website: http://www.sailorenergy.net/Minerals/MineralMain.html

Original article follows:

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

Unexpected Geode Find! from Thomas Farley on Vimeo.


Under SW UV, Along With My First Brachiopod (Shell)

Unexpected Geode Find Under Shortwave UV from Thomas Farley on Vimeo.


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.


35.830022, -115.285060

Jean Quad


Follow me on Instagram: tgfarley


Hawaii In A Bottle

Self collecting is great but most of us can’t go around the world to chase specimens or go back in time to get them. Case in point is this old stock Hawaiian sand from Geological Specimen Supply, mentioned in my last post.

This sand is over twenty years old, predating the ban on removing sand from the Islands.  This specimen comes with great labeling, a summary of the fuller descriptions RC provides on his site. Did you know that Waikiki’s beaches actually came from Long Beach, California? Read on and then take a look at what I am seeing under my scope.

“Sand is derived from whatever material is locally available. Beaches are uncommon on the seacliff-ringed Island of Hawaii. Occasional small coves have sand derived primarily from basalt unless there is a coral reef offshore. This sand was collected from a small cove near South Point, Hawaii, where a local concentration of cobbles of basalt and coral was the source material for this sand. The sand is primarily coral and basalt, giving it a salt and pepper look, with occasional small shell fragments adding variety to the mix.”

“Hawaii’s white sand beaches at Waikiki were initially an import, from California. In the 1920s and 1930s sand was barged from Long Beach, though the import of California sand was abandoned in the 1970s and the beach is now maintained with locally dredges sand composed of coral and shell fragments. A locally famous black sand beach occupies a cove southwest of Hilo, where the sand is entirely basalt. At Mahana Bay, near South Point, the greenish sand is composed of grains of olivine that weather out of the basalt.”

“Set of five tubes, 16 ml each, optically clear polystyrene with screw caps. The plastic tubes are practical in a classroom and are somewhat student resistant, though a cap can be unscrewed. Good for student examination. When this sand is gone, it’s gone. A recent law prohibits removal of sand from Hawaii’s beaches.”

The focus of our attention.

Here are images just taken under my microscope. These are single focus shots, so the foreground and background focus aren’t the same. Really good photographers take a number of shots at different focal points and then have software combine them to produce a perfectly focused imaged. I’m trying to learn to do that.

White material is probably coral, dark material basalt, and the green is olivine or peridot. Shell fragments, too. Olivine is thrown out from deep within the earth during volcanic eruptions, mixed up with basalt at the same time. Basalt pieces can make up a black sand beach, the lighter peridot may weather out of the basalt and collect together, producing a rare green sand beach.

Closeup of a peridot or olivine grain, exhibiting poor conchoidal fracturing.

A shell, sharpened in Photoshop.

Unsharpened and from a different angle. Any difference?

Another shell, this one red.

Basalt with olivine from the San Carlos Apache Reservation in Arizona. This is what tribal member Stevie Joey mines on his peridot claims. His site is Peridot Dreams and you can learn all about gem grade peridot there. He is receptive to inquiries about touring his claim.

Specimen tube. Buy several to trade.