[Rockhounds] Coating on rocks near Globe, AZ

[Jim Murowchick]

We just found one such piece in a donated collection--the substrate looks
like it is a chunk of mortar or concrete (though not much can be seen)
coated with what was labeled as malachite. When we ran the XRD, it turned
out to be brochantite and nothing else.  I don't think there was a location
given with the sample, though.


Jim Murowchick
UMKC
Kansas City, MO


On 11/25/08 11:26 AM, "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....
> 
> 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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