"Terlingua-type" Calcite with Unusual Yellow Midwave UV Response

Contributed by: FMS Admin
minID: 8C2-14D
Date: May 15th, 2026
Locality: Challenger Cave System, Monterrey Municipality, Nuevo León, Mexico (See on Mindat)
Size: 6.2 x 3.8 x 8.4 cm

Description:
A few months ago, I purchased this nice and big cleavage rhomb of "Terlingua-type" calcite, from the Challenger Cave, Nuevo Leon, Mexico. Took me a while before shooting and posting it, since I waited until receiving my new spot cleaning gun to remove some unsightly bruising on some of its edges (these small cleaning guns, with the nozzle adjusted to generate a thin "needle jet" are powerful enough to remove bruises and chisel marks - any perfectionist collector should get one). The fluorescent intensity is reduced in bruised areas, and bruised specimens do not look good in daylight in my opinion. Some imperfections remain, but the specimen is in much better shape now than it was when I received it.

While not being as gemmy as I would like it to be, it's still a really lovely piece, both under various UV wavelengths and in visible light; and its yellow response under midwave UV is really nice. As usual, it reacts not only to UV light but also to blue light and green light; I did not include pictures of the green and blue light responses, but will eventually, as soon as I have the required filters. But, instead, I shot it not only under 365 nm longwave UV but also under 395 nm LW UV; the response under this wavelength is yellowish cream white. Under 450 nm blue light it is bright yellow. The response to green light is orange red; it is easier to observe with a green laser and does not require filters.

Originally posted by Frédéric Messier Leroux on Nature's Rainbows in 2021.