Tuesday, September 27, 2011

UV Fluorescent Brachiopods

This fossil plate of a cluster of Sowerbyella (Jones, 1928) brachiopod shells appears to have a unique property of fluorescence under longwave ultraviolet light (394? nm).  My light produces a lot of visible purple light so the specimen appears quite purple with some orange-brown color on some shells.  In person, the orange-brown color is much more pronounced.

I believe the mineral present is aragonite with a manganese activator.  Referring to the book The Uranium and Fluorescent Minerals: A Handbook of Uranium Minerals and A Field Guide for Uranium Prospecting 3rd Ed. by H.C. Dake, page 21, it lists "ARAGONITE. A calcium carbonate that fluoresces and phosphoresces variably.... When manganese is the chief activator the luminescence is orange or red-orange, and usually faint."

These fossils are from the Kope Formation (Edenian Stage, Upper Ordovician Period) of Kentucky USA and that layer is known for its aragonite fossils (usually brown).  I need to now go through the collection and test them for fluorescence.

Another issue I need to solve is filtering visible purple light from my UV light. I might have to go Thomas Edison on it and just start trying different materials for filtering properties.