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GeneralSugar Grove, WV nontronite vs kaolinite

2nd May 2019 17:28 UTCPatrick Haynes (2) Expert

Having collected at Sugar Grove I have sometimes opened wet vugs, with bright green (!) nontronite. The watery solution leaks out and, within a day or two, the nontronite turns black. Quickly tossing a freshly exposed nontronite coated vug into a container with water does not stop the color change. The color change must be due to dehydration, oxidation, or the absence of its accompanying solution, and whatever chemicals it contains. Comments?


Black nontronite often coats vugs and other minerals, including pyrite , however there is another mineral that also often coats minerals: gray kaolinite. I often see specimens and images of kaolinite coating pyrite labeled as "nontronite on pyrite". Any comments pro or con? Note: In past years I have had xrd confirmation of both.

2nd May 2019 18:37 UTCTom Tucker

The color change in nontronite has been discussed, and experiments conducted. It is a photo-reduction reaction, and can not be reversed once it's exposed to light.

How do you know the light colored material is kaolinite ??

2nd May 2019 23:00 UTCPatrick Haynes (2) Expert

xrd
 
and/or  
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