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Techniques for CollectorsCleaning iridescent hematite (turgite) coatings

10th Nov 2010 14:17 UTCJohn Lichtenberger

I have a bunch of iridescent hematite from both Graves Mtn (Ga.) and Willis Mtn (Va) that I'm trying to clean to maximum effect. Several pieces have what appears to be a highly colorful layer beneath the surface, which can be exposed by careful prying and chipping, but it's a hit or miss operation trying mechanical cleaning. I've tried bisulfite/citric acid mixes with some success, but sometimes the color is removed as well...

The overlying coating appears to be goethite/hematite with a metallic coppery to brownish color, and itself slowly becomes iridescent with careful hand cleaning (as on the lower left section below) . HCl and strong SIO remove the iridescence

Photo not the best, taken under flourescent tube lighting at nite... colors really "light up" in daylight

http://i3.photobucket.com/albums/y62/auplater/TURGITE2.jpg

any ideas on chemical cleaning methods to enhance/expose the desired colors?

auplater

10th Nov 2010 21:18 UTCRock Currier Expert

John,

Iridescence is usually the results of thin mineral films on the surface of minerals and with very little effort you can probably clean it right off your specimens, so "careful" is the key word here. I suspect that the cleaning procedure may be dependent on what is causing the iridescent at each locality at which it is found. I predect you will have a lot of experimentation in your future. When you think you know what is going on I would appreciate if you would check back in here and tell us what you learned.