[meteorite-list] NEW photos of the silicated iron... Chrome Diopside

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Fri Nov 10 21:56:55 2006
Message-ID: <17589.82351.qm_at_web51011.mail.yahoo.com>

--- MARK BOSTICK <thebigcollector_at_msn.com> wrote:
 I was wondering on the chromium aspect. I
> know some of you are better geology people then me,
> but wouldn't that be an emerald?

 Chromium is one of the trace elements responsible for
the "green" color in both diopside and emerald.

Basic Diopside is ((Ca,Mg)Si2O6), Calcium Magnesium
Silicate:an Inosilicate--(Single Chain)--a Pyroxene if
you will, which is a class of minerals well
represented in meteorites. Chrome diopside
((Ca,Na,Mg,Fe,Cr)2(Si,Al)2O6) is heavy in Cr and Fe.

The existence of diopside in a meteorite is
significant from a mineralogical standpoint owing that
the ratios it forms with other pyroxenes above 900?C
and below 700?C limit the situations where it can
occur as large crystals.

Emerald is the gem name for green beryl:
Be3Al2(SiO3)6, Beryllium Aluminum Silicate, which is
an which is a Cyclosilicate-Ring Silicate. Beryl, in
any form, has not been found in meteorites(AFAIK).
Beryl is rare anyway owing that the beryllium and
chromium are usually scavenged away in formation. Thus
it can only form emerald under very specific and rare
conditions. Were it not for the beryllium these
molecules would be pyroxene chains instead of rings. A
cyclo-silicate is a chain silicate that links back on
itself to form rings.

As such, the two minerals are distantly related but
form in very different environments. Scientifically
interesting but probably mundane for the lay
collector, by working backwards from the minerals
found in meteorites we can understand the conditions
in which they formed(composition, temperature, and
pressure).

Elton
Received on Fri 10 Nov 2006 09:56:43 PM PST


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