Recent Field Trip Update

Been waiting on others for help with identification of tiny crystals found in tuff near Jean, Nevada on a recent field trip. Thought it chabazite at first through photos but that material is too soft at 4.5 to 5 on the Mohs scale. My crystals are at six.

Wendi with Minerals Unlimited sent me some chabazite but it does not match up to what I have. Tried sending a sample to Kaygeedee Minerals in Canada for testing but DHL has held up my package. Called immediately after they called and got a recording that said they were closed for the day. More waiting.

Here’s what tuff looks like in a video, although it can take on many forms. I have five reference samples. As you can tell with common tuff, weathered surfaces are deceiving. Freshly broken surfaces reveal an ash gray color.

Tuff Near Jean, Nevada from Thomas Farley on Vimeo.

And here I am at point of discovery, thinking I had stumbled upon quartz crystals. This area had gotten much richer in mica as I walked toward it, indicating increased mineralization.

Sanidine crystals in tuff? Near Jean, Nevada from Thomas Farley on Vimeo.

Hand samples.

And here are what a beat up crystal looks like. Too often mineral books want you to find a perfectly shaped crystal for identification. This is what you usually find. The clue here, though, is conchoidal fracturing, which does help with ID.

These are my mineral choices according to the text of the Jean geologic quad. It is often extremely difficult to determine what a rock or mineral is if it is outside of a mining district or away from a described mine. I had a similar experience near Plymouth, California with an outcropping of massive botryidal hematite and goethite that took nearly a year to of persistence effort and many experts to identify.

“Tb Tuff of Bridge Spring (middle Miocene, 15.2 Ma) (Faulds et al., 2002a, b) Purplish-gray to light-gray, weathering pale-brown, moderately to densely welded rhyolitic ash-flow tuff containing 10–15% anhedral to subhedral phenocrysts of sanidine and significantly lesser amounts of biotite, clinopyroxene, plagioclase, hornblende, and distinctive, honey-yellow sphene. Lithic fragments (~1%, <5 mm) of reddish and dark-gray intermediatecomposition volcanic rock and lesser granitic rock. Basal dark-gray vitrophyre commonly found at base. Weathers to rounded boulders. Distinguished from Tmd by presence of ubiquitous sphene and somewhat smaller sanidine phenocrysts. Appears to have accumulated in a northeaststriking topographic low defined by the underlying Trg. Thickness 0–25 m.”


I hope to update this post as I get more information. Just waiting on others. And the postal system and DHL.


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