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PhotosAndersonite - D-Day Mine group, Thompsons District, Grand Co., Utah, USA

25th Apr 2019 10:37 UTCChristian Auer 🌟 Expert

Andersonite

D-Day Mine group, Thompsons Mining District, Grand County, Utah, USA

And the main - white - mineral is gypsum?

25th Apr 2019 19:08 UTCPaul Brandes 🌟 Manager

More than likely, yes.

25th Apr 2019 21:25 UTCRick Dalrymple Expert

Probably gypsum but it looks like it could be aragonite.

27th Apr 2019 09:12 UTCDan Polhemus

As far as I can determine, the paragenesis here is andersonite over gypsum, on sandstone. Both of these minerals form as efflorescences on the walls of old uranium mines. Andersonite is not recorded from the D-Day Mine Number 4 tunnel in Mindat, but should probably be added there, because I have no reason to doubt the Michael Shannon label that came with this specimen, which specifies that locality. In addition, someone else has already posted a previous photo of andersonite from D-Day Number 4, so the evidence seems to be accumulating.

Andersonite has a yellow-green glow to it that simply looks radioactive, and it is, although only moderately so. This specimen returns a reading of 550 cpm at 1 cm using my cheap GMC-300E Plus geiger counter from Amazon. Nothing to run away from, but I wouldn't keep it in my pocket all day.

The specimen is also strongly blue-green fluorescent under long-wave UV light, as per the attached photo.

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