[meteorite-list] Diogenite Nomenclature

From: barrat at univ-brest.fr <barrat_at_meteoritecentral.com>
Date: Sat, 15 Sep 2012 23:16:09 +0200
Message-ID: <1347743769.5054f019a9173_at_webmail-sdt.univ-brest.fr>

Hi Mike,

No. The "Olivine diogenites" do not display systematically a texture different
to that of regular diogenites. Tatahouine is not a correct example because it is
unbrecciated and have very large crystals. The largest I have seen is 5 cm in
length! Tatahouine is unique. NWA 5480 is exceptional too, but of course
different to Tatahouine. If you compare two brecciated diogenites, one with
olivine, the other devoid (or nearly devoid) of olivine, (e.g., Roda with
Johnstown), you cannot tell with the hand specimens which one is the "olivine
diogenite". You need polished sections.

You are certainly able to distinguish NWA 1877, from NWA 5480, Bilanga and
Tatahouine. They are different rocks with particular aspect. It is not so simple
with all the diogenites!

Cheers

Jean-Alix



Selon Galactic Stone & Ironworks <meteoritemike at gmail.com>:

> Hi Diogenite Fans,
>
> Any time we have a discussion about diogenites, I look forward to Doug
> Dawn's input. Calling Mr. Dawn, calling Mr. Dawn..... :)
>
> >From a layman's standpoint, the difference between olivine diogenites
> and "regular" diogenites is easy to see in a hand specimen. The
> texture of an olivine diogenite is quite different than what we see in
> classic diogenites like Tatahouine and Johnstown. One look at NWA
> 5480, NWA 1877, or any other OD, and it's easy to see that there must
> be a compositional difference between these OD's and other diogenites.
>
> I have some unclassified samples which reportedly came from the same
> finder and strewnfield as NWA 5480. They are too small to have
> classified on their merit, but even in pieces that are only 1 or 2
> grams, their unique texture and character is evident. To my eyes (and
> microscope), these unclassified pieces are obviously from the olivine
> diogenite family. Can I prove it with lab data? No. But they are
> fun to look at. :)
>
> At any rate, from a collector's standpoint, I think OD's should be
> distinguished from the "regular" diogenites. Anyone who has owned or
> handled a sizeable chunk of OD (with that delicious fusion crust that
> is rarely seen), knows it is something special deserving of it's own
> classification.
>
> Best regards,
>
> MikeG
>
> --
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>
>
> On 9/15/12, barrat at univ-brest.fr <barrat at univ-brest.fr> wrote:
> > Hi,
> >
> > the "problem" of the taxonomy of diogenites has been discussed recently in
> > this
> > paper:
> >
> > Andrew W. BECK and Harry Y. McSWEEN Jr (2010),Diogenites as polymict
> > breccias
> > composed of orthopyroxenite and harzburgite, Meteoritics & Planetary
> > Science,
> > Volume 45, Issue 5, May 2010, Pages: 850?872,
> > DOI: 10.1111/j.1945-5100.2010.01061.x
> >
> > The authors have proposed an adaptation of the classical classification of
> > terrestrial ultramafic rocks. I agree with their suggestions. Depending of
> > the
> > proportion of olivine, harzburgitic diogenites and dunitic diogenites can
> > be
> > defined.
> >
> > The difficulty of the classification of diogenites is the size of the
> > samples
> > used by classifiers. These lithologies are often extremely heterogeneous,
> > and it
> > is often not possible to determine accurately the proportion of olivine
> > using a
> > single polished section. Anyway, the problem of taxonomy is not a critical
> > scientific issue. Of course, it is important to determine the abundance of
> > olivine in a diogenite, but this proportion does not change the
> > interpretation
> > we have on these rocks. At present, all the diogenites which have been
> > investigated in depth, are cumulate rocks, certainly coming from a number
> > of
> > intrusions. These intrusions contain certainly different types of rocks,
> > including regular diogenites and olivine bearing diogenites. For example,
> > trace
> > elements indicate that NWA5480 and Tatahouine come probably from the same
> > intrusion... Not from the mantle of the parent body.
> >
> > Cheers
> >
> > Jean-Alix
> >
> >
> >
> > Selon Greg Hupe <gmhupe at centurylink.net>:
> >
> >> Dear List Members and fellow diogenite enthusiasts,
> >>
> >> I talked with Tony Irving this morning regarding the use of 'Olivine
> >> Diogenite' in classifications and abstracts. I have been enlightened to
> >> the
> >> ever evolving diogenite classification scheme. Seems a new 'pigeon hole'
> >> has
> >> been created due to new meteorites which are comprised of mostly olivine,
> >> the
> >> Dunite meteorites. Find below Tony's reply and link to an abstract that
> >> discusses their proposed, and more accurate separation of the Diogenite
> >> meteorites.
> >>
> >> Best Regards,
> >> Greg Hupe
> >>
> >> Begin forwarded message:
> >>
> >> > Hi Greg:
> >> >
> >> > Here is a link to the abstract for our presentation in London last
> >> > year.
> >> Most people seem to like this proposed scheme
> >> http://www.lpi.usra.edu/meetings/metsoc2011/pdf/5223.pdf ... [NWA 1877,
> >> NWA
> >> 5480 and other similar meteorites] would now be harzburgitic diogenites,
> >> but
> >> olivine diogenite is still OK as a general term. The nature of
> >> nomenclature
> >> is that it evolves with the need to encompass new specimens, and we have
> >> mostly NWA and private collectors to thank for that.
> >> >
> >> > Cheers,
> >> >
> >> > Tony
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Received on Sat 15 Sep 2012 05:16:09 PM PDT