[Rockhounds] Cookeite

Tue Oct 6 09:20:31 PDT 2020

Thanks Andrew.  I guess I'll set the jar on a shelf and let my son figure
out what to do with it when I'm gone.

With Appreciation & Gratitude,
Stuart Schmitt
Clear Creek Crystals
60 Mary's Eagle Trail
Mt Ida, AR 71957
(870) 867-2443
www.arcrystalmine.com

-----Original Message-----
From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> On Behalf Of
Andrew Turner
Sent: Monday, October 5, 2020 1:15 PM
To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
<rockhounds at rockhounds.drizzle.com>
Subject: Re: [Rockhounds] Cookeite

Cookeite is a lithium mica, although it is part of the chlorite group.
Unfortunately, there are numerous lithium micas that are extremely similar
with only small variabilities in the elemental substitutions and solution
series.  If I remember, the lithium mica (e.g. lepidolite) phase diagram has
something like 17 end members, although I know they've tried to clean this
up and better organize this group.

So, EDS will not work (it will show a lithium mica).  XRD may work if it is
pure cookeite, although single crystal XRD would be the best.  Microprobe or
Raman may work as well.

The real question is whether it is worth going through all of this to
positively identify the mineral, which still may not be possible.  Cookeite
in itself has very little value especially since it isn't all that uncommon,
crystals typically aren't colorful or really unusual, and crystals are
almost always micro.  I did find a photo of cookeite from that quarry, and
it is associated with quartz (not surprisingly given the site).  In
California, you do get cookeite associated with elbaite (tourmaline) from
the Himalaya Mine and other pegmatites.  The cookeite adds contrast and
associations to the main mineral which does increase the value, but it
usually isn't very valuable by itself.

You probably do have cookeite (or a very similar lithium mica) based on the
location and associations.  I don't think there would be an issue labeling
it as that.  Thank you.

Andrew Turner
Salt Lake City, UT

________________________________
From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> on behalf of
DON HALTERMAN <donhalterman at comcast.net>
Sent: Sunday, October 4, 2020 4:29 PM
To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
<rockhounds at rockhounds.drizzle.com>
Subject: Re: [Rockhounds] Cookeite

Looks like XRD would be the best bet.  The lithium and (OH) make positive ID
by EDS difficult. I don't know what other minerals have similar formulae,
but for a solid positive ID I'd get x-ray diffraction patterns coupled with
chemistry by wavelength dispersive spectroscopy or perhaps Raman
spectroscopy.

> On 10/04/2020 3:02 PM stu at arcrystalmine.com wrote:
>
>
> I have a pint jar full of what I believe to be yellow/gold color 
> cookeite micro crystals from Jeffrey Quarry, near North Little Rock, 
> Pulaski County, Arkansas.  Does anyone have the capability of testing 
> the crystals to confirm it is cookeite and is there any value in the
cookeite?
>
>
>
> With Appreciation & Gratitude,
>
> Stuart Schmitt
>
> Clear Creek Crystals
>
> 60 Mary's Eagle Trail
>
> Mt Ida, AR 71957
>
> (870) 867-2443
>
>  
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