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Prehnite color variables

Posted by gary moldovany  
gary moldovany December 15, 2011 01:34AM
I have many specimens of prehnite from NJ and elsewhere. I have yellow, white, the usual green and some light blue. Does anyone know what causes the color variations in this mineral? Thanks. Gary
Warren Cummings December 15, 2011 02:51AM
There was a paper on this subject by Kurt Nassau, of Bell Labs, in the 1970's. Versions of various technical depth appeared in at least 2 or 3 journals as I recall. The first one I saw was in Scientific American. As I remember there are basically 2 causes: (1) inclusions and (2) transition metal elements either as major or trace components. Without reviewing this, and perhaps other literature, I'd guess that prehnite color is due to minor amounts of things like iron or copper or vanadium, whatever was around in the depositional environment that could find a home in the prehnite structure.
Hershel Friedman December 15, 2011 04:51AM
There is a rare pure white Prehnite from the O&G Quarry in Connecticut, which would indicate that the green color exhibited in most prehnite is caused by impurities, and green isn't the inherent color. I have heard once that iron impurities are responsible for the green, but this is unverifiable as I don't recall the source.
Henry Barwood December 18, 2011 11:29PM
Many years ago, veins of colorless prisms of prehnite were common at the Foote Mine near Kings Mountain, NC. Wish I had saved a few, but they were so common few people collected them. I've found a few stout, very pale green prisms in explosion breccias at the 3M Big Rock Quarry near Little Rock, Arkansas.

Henry Barwood
Troy University
Troy, Alabama USA
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