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Curious Mind: Volcanic glass shards formed in an air after explosion

Curious Mind: Volcanic glass shards formed in an air after explosion

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Q: I’m curious about what the bright white material along Highway 93 cut just north of Contact, Nevada, might be. Is it diatomaceous earth or something else?

A: “I know the road cut outcrop of which you are speaking,” said Art Small, a geologist from Murphy Hot Springs. “I was curious about it, hoping that it was zeolite, or diatomaceous earth. Upon looking at it with a microscope I found that it is primarily composed of volcanic glass shards, pumice in common terms. It formed as an air fall event from a rhyolitic volcanic explosion, probably in the Jarbidge area. The red hot ash cloud from the explosion cooled quickly in the atmosphere, forming glass similar in composition to obsidian.”

“There are a few buildings at the San Jacinto ranch constructed of blocks carved from this formation,” Small said. “Old timers carved their names in the blocks.”

“I have been retired for a while. I have a bachelor’s of science in geology from Colorado State University, and worked exploration and production geology for several mining companies for 36 years in the U.S., Mexico, Chile, and Argentina. I am not certified in Idaho so I cannot do any contract or consulting geology work in Idaho.”

“Diatomaceous earth is composed of very small silica spheres which were the shells of very small lake dwelling animals. The silica for their shells is usually obtained from dissolved silica from rhyolitic ash falling on a lake. Diatomaceous earth is mined commercially near Lovelock, Nevada, and is used in filters.”

“Zeolite is a clay mineral also sources from rhyolitic volcanic ash. It is used in ionic filtering units such as water softeners,” Small said.

Have a question? Just ask and we’ll find an answer for you. Email your question to Kimberly Williams Brackett at with “Curious Mind” in the subject line.


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