image banner

SC313 - Yellow Chalcedony

Locality: Milwaukee Co., Wisconsin, USA (MINDAT)
Size: 5 x 4 x 4 cm - Miniature (3-6 cm)
Weight: 94 g
minID: N1U-HQ7

This was collected in northern Milwaukee county along the beach at night. The exact location is not known but it may have been north of the Schlitz Audubon nature center. I’ve been told these chalcedony nodules are fairly common and have varying degrees of fluorescence, most are a dull yellow tan to a dull orange in color and some show no fluorescence. The element/mineral that causes the fluorescence is not known, but it could be carbonate. On the lake Michigan beaches you can find chalcedony after carbonate pseudomorph of Favosites and Halysites corals and, though this one is not an obvious former fossil, it does have some interesting patterns/structure that make it a possibility. The fluorescent spectrum under 365nm LED shows a broad, composite band centered at about 570nm. Not sure about the activator… Probably carbonates and organic compounds.

Photo in normal light.
Fluorescence under longwave UV light (365nm LED).
Last update: 29 December 2020