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SC283 - Hourglass Gypsum

Locality: Chodziez Co., Greater Poland Voivodeship, Poland (MINDAT)
Size: 6.5 x 2 x 1 cm - Small cabinet (5-7 cm)
Weight: 12.4 g

Hourglass gypsum/selenite. While clear in white light, it shows a fluorescent hourglass pattern under UV light. Probably due to selective inclusion of impurities (hydrocarbons?) along crystallographic faces during crystal growth. Major diagonal is 6cm long.

Fluorescence spectrum under 275nm LED. The blue fluorescence color is due to the broad peak between 400nm and 500nm. The sharp and intense peak at 339nm (which looks like to be a doublet) was a surprise. I don’t know what is the cause.

Photo in normal light.
Fluorescence under longwave UV light (365nm LED).
Fluorescence spectrum under shortwave UV light (275nm LED).
Last update: 31 December 2020