[Rockhounds] Coating on rocks near Globe, AZ

[Al Balmer]

On Tue, 25 Nov 2008 12:26:48 -0500, "R. Peter Richards"
<rpr at heidelberg.edu> wrote:

>The obvious guess would be malachite, but there are several other  
>copper secondary minerals that would be possibilities.  Given your  
>observations, it would be an interesting experiment to turn over some  
>of the rocks, and see whether the green that is exposed goes away and  
>whether the previously exposed part becomes green.  And how long it  
>takes....

I can answer part of that question - I have some that was collected
two years ago and is still green. On one specimen which is broken, the
coating appears to be 0.4-0.5mm thick. The rock inside is a uniform
light gray, fairly fine-grained. I think it's a short-term process,
since the half-covered ones are in a graded roadway. I don't know
graded how long ago, but years rather than centuries.

>
>Pete Richards
>
>
>On Nov 25, 2008, at 12:22 PM, Al Balmer wrote:
>
>> On the west side of Globe, there's an area on the edge of a mine dump
>> which has common stone covered with some green copper mineral. This is
>> evidently a short-term process, since rocks half-buried in the dirt
>> have the coating only on the covered part.
>>
>> I'm curious as to what the coating is, and what the mechanism is.
>> Anyone know?
>>
>> -- 
>> Al Balmer
>> Sun City, AZ
>>
>> -- 
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>___________________________________
>R. Peter Richards
>rpr at heidelberg.edu
>Morphological crystallographer
>
>
>
>
>
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-- 
Al Balmer
Sun City, AZ