[meteorite-list] Density of Greg's gorgeous new NWA 3149 howardite

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:58 2005
Message-ID: <DIIE.0000000000003543_at_paulinet.de>

Greg wrote:

> Due to huge interest and near buy-out of my new Brecciated Howardite,
> NWA 3149, I listed on eBay last night, I have listed eight more slices
> today.

> NWA 3149 is a brecciated and highly shocked howardite and has got to
> be the most dense howardite I have ever cut and polished. I used up a
> new blade and it took eight hours to polish the slices from the 1500-gram
> stone ...

John inquired:

> Could it be source depth or are all howardites
> derived from relatively shallow depths?

Hello John, Greg and List,

Yes, all howardites should have been derived from *relatively* shallow depths
as they are "polymict breccias composed of clasts of diogenite- and eucrite-
like material and appear to have formed largely as mixtures of diogenites and
eucrites in the *regolith* of the HED parent body."

Reference:

RUZICKA A. et al. (1997) Vesta as the howardite, eucrite and diogenite parent
body: Implications for the size of a core and for large-scale differentiation
(Meteoritics 32-6, 1997, 825-840, p. 825).

What may have made it so dense? Maybe the combination of shock and heat?!

(Impact) shock will surely help in compacting and in consolidating matrix
components (unless the shock is so gigantic that the impacted material is
pulverized).

Impacts cause heat, so let's have a look at part of its mineralogical
analysis: "... ilmenite (one with a *b a d d e l e y i t e* inclusion)"

The presence of baddeleyite (ZrO2) is extremely interesting. Only rarely will
you find it in HEDs whereas it is a frequent minor phase in lunar meteorites
and SNCs (along with ilmenite) due to lunar and martian shock events.

Alan Rubin writes:

"Baddeleyite ... forms by thermal decomposition of zircon at
very high temperatures (ca. 1680?C) and low ... pressure ..."

Reference:

RUBIN A.E. (1997) Mineralogy of meteorite groups
(Meteoritics 32-2, 1997, 231-247, p. 242).

So NWA 3149 must have endured high shock pressure + very high
temperatures, which may have led to this compaction of its matrix
material(s).

Howarditically
yours,

Bernd
Received on Thu 17 Mar 2005 03:36:46 PM PST