Ilion Gorge Fluorescence

WCGMC News article for September, 2015 –  By Ken St. John

My son, Isaac, and I joined the club on the field trip to the Jerusalem Road Gorge in Ilion earlier this year (see July 2015 WCGMC News).  In sorting through the material we brought back (yes, we left the deer skeleton) I exposed the rocks and minerals to UV light.  I thought that I’d share the pictures.

Our first find was some calcite that Isaac retrieved from the opposite side of the gorge.  The piece is interesting in daylight for all of the calcite formations and patterns, but exposure to Short Wave UV really gets your interest.  Calcite often fluoresces and we’re used to seeing the bright orange / red fluorescence from Sterling Hill and Franklin, New Jersey and from Eganville, Ontario.  As shown below, the Jerusalem Hill calcite fluoresces brightly blue/white.

The specimen above measures roughly 5 inches in both directions and is 1.5” thick.

The specimen above measures roughly 5 inches in both directions and is 1.5” thick.

The real surprise came when I lamped a piece of the satin spar gypsum that Matt Weiler had discovered in the shale bank just downstream from the main travertine area.  As seen below, the gypsum which is bright white in daylight glows blue in UVA light.

The gypsum piece is 4” long, 3” deep and 1.5” high.

The gypsum piece is 4” long, 3” deep and 1.5” high.

I used a powerful UV display lamp set close to the specimens to obtain these photographs.  There is a bit of the violet of the lamp reflected by the gypsum (center bottom of the picture).  The gypsum benefits the most from higher power as its fluorescent response is maybe half that of the calcite.

An Ilion stalactite:  Some of the “caves” or openings in which the travertine grows in Ilion Gorge can be rather large.  This 9” piece was wrestled out of its home in 3 pieces and repaired (note the arrows).

An Ilion stalactite: Some of the “caves” or openings in which the travertine grows in Ilion Gorge can be rather large. This 9” piece was wrestled out of its home in 3 pieces and repaired (note the arrows).

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