[meteorite-list] Color of OC's by Staining or by Trace Elements

From: Laurence Garvie <lgarvie_at_meteoritecentral.com>
Date: Wed, 30 Mar 2011 23:30:06 -0700
Message-ID: <E2C494A3-8A3F-47F9-8570-B81EEBEBF987_at_asu.edu>

Just a quick reply to this subject as it could become lengthy and involved.

The primary coloring agent in meteorites is Fe2+ for fresh meteorites and Fe3+ for weathered ones (BTW - shocked meteorites can be black - see below). There is also Fe0, which is in the metal.

When a few percent of Fe2+ is present, then minerals such as pyroxenes and olivines are usually green to greenish-yellow. A good example of Fe2+ coloring is in Johnstown, which is composed primarily of green pyroxene.

If very little Fe2+ is present then pyroxene is normally white/clear as in the aubrites, such as Bishopville.

In our oxidizing atmosphere, the metals in meteorites rust, producing Fe3+ -bearing oxides/oxyhydroxides. These rust minerals stain the meteorite and can range in color from yellow-orange-red-purple-brown-black.

Shocked meteorites can be black. A great comparison is between the two know chassignites - Chassigny and NWA2737, both of which have similar mineralogies. Fresh Chassigny is yellowish green - the color is caused by Fe2+ in the olivine. Yet, NWA2737 is black. The black color is caused by abundant 5 to 15 nanometer-sized iron-nickel droplets in the olivine, which are strongly absorbing in the visible and near-IR region of the spectrum. These droplets are formed during intense shock events.

Practically everything you ever wanted to know about color in minerals can be found at Prof. Rossman's site at http://minerals.gps.caltech.edu/


Laurence
CMS
ASU

On Mar 30, 2011, at 7:52 PM, meteorite-list-request at meteoritecentral.com wrote:

> essage: 3
> Date: Wed, 30 Mar 2011 12:20:31 -0400
> From: Michael Gilmer <meteoritemike at gmail.com>
> Subject: Re: [meteorite-list] Color of OC's by Staining or by Trace
> Elements
> To: Thunder Stone <stanleygregr at hotmail.com>
> Cc: meteorite-list at meteoritecentral.com
> Message-ID:
> <AANLkTin9FfUsroBhMrVFDfH1_GCoss3B3L-vFf9zJ6T_ at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi Greg and List,
>
> Great question Greg. I'm curious to hear what the experts have to say.
>
> Some OC's start out as white or light-grey - like some LL6 types.
> That is why some LL6 meteorites are mistaken for lunars or eucrites -
> because they lack chondrules and have that whitish color.
>
> Best regards,
>
> MikeG
>
> ----------------------------------------------------------------------
> Mike Gilmer - Galactic Stone & Ironworks Meteorites
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>
>
> On 3/30/11, Thunder Stone <stanleygregr at hotmail.com> wrote:
>>
>> Hi List:
>> I hope everyone is well.
>> I have a question regarding the 'color' of OC's through staining by some
>> mineral influx or by oxidation. It appears most fresh OC's start out as a
>> light beige or tan color; then through time the metal rusts and they often
>> turn yellowish, orange, or brownish - this make sense. My questions is
>> this:
>> What other colors can they become, blue or green? What element(s) result in
>> different colors? What different weathering processes are involved?
>> The reason I ask is because I have a weathered meteorite that is dark green
>> in color; it looks like jade and I have not seen any like this one before.
>> I have also and seen OC's with a 'black' color, what causes that?
>> Thanks,
>> Greg S.
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> --
>

-----------------------------------------------------------
Dr. Laurence A.J. Garvie
Collections Manager
Center for Meteorite Studies
School of Earth and Space Exploration
Arizona State University
Tempe
AZ 85287-1404
USA

phone: 480 965 3361
fax: 480 965 8102
email: lgarvie at asu.edu

Weblinks:
School of Earth and Space Exploration: http://sese.asu.edu/
Center for Meteorite Studies: http://meteorites.asu.edu/

-----------------------------------------------------------
Received on Thu 31 Mar 2011 02:30:06 AM PDT