[meteorite-list] Weathering Grade

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:46:25 2004
Message-ID: <3B0596A7.252BF03E_at_lehrer1.rz.uni-karlsruhe.de>

Ron wrote:

> DaG 276 Eucrite is listed as a W3
> HaH 193 (Winonaite) also as a W3

> Am I on track here?


Hi All!

Yes, you are on track, at least with regard to the entries
because I have the same weathering categories, but, on
the other hand, remember what Jeff wrote:

> You can consider weathering grades less than 5 (where silicates get
> altered) of metal-poor meteorites to be basically useless numbers.

So he might be able to explain why a few achondrites were given
weathering categories if these numbers are "basically useless".
Such examples are:

Dar al Gani 411, eucrite => W0
Dar al Gani 567, eucrite => W1
Dar al Gani 609, eucrite => W2
Dar al Gani 844, eucrite => W3
Dar al Gani 779, howardite => W1

Hammadah al Hamra 059, eucrite => W3
Hammadah al Hamra 261, eucrite => W0
Hammadah al Hamra 262, eucrite => W0

Steve wrote:

> Could you possibly give example meteorites and their weathering grade?
> what would the weathering grade of say, Huckitta, Wolf Creek,
> or Camel Donga?? Stones vs Irons? Pallasites vs Achondrites?

I can't for these cases because Wlotzka explicitly states that
his weathering scale can only be applied to the o r d i n a r y
chondrites.

WLOTZKA F. (1993) A weathering scale for the o r d i n a r y
chondrites (Meteoritics 28-3, 1993, A460)

> A researcher at UCLA told me that weathering grades
> only apply to chondrites with metal grains.

... this makes sense and it would also underline
both Jeff's comment above, and Bob's words:

> I have no idea how it could be applied to any Stony
> [i.e., eucrite] w i t h o u t metal grains.

Ron also wrote:

> HaH 193 (A Winonaite) also as a W3

Probably it is possible to accord a weathering grade to some of the
winonaites because of their relation to IAB irons. Winona itself is
reported to contain sufficient heavily weathered metal [HERZOG
G.F. et al. (1993) 26Al and 10Be activities of Lodranites and
Winona (Meteoritics 28-3, 1993, A362-A363)].

Jeff also mentioned:

> Eucrites DO contain metal and sulfide, albeit not much.

NORTON O.R. (1998) Rocks From Space, 2nd edition, pp. 205-206:

The pigeonite matrix usually contains tiny grains of
iron metal, making these meteorites slightly magnetic.

References:

DUKE M. (1965) Metallic iron in basaltic achondrites
(J.Geophys. Res.70, 1523-1527).

PALME H. et al. (1988) Camel Donga: A eucrite with
high metal content (Meteoritics 23-1, 1988, 49-57).

JACKSON H.S. et al. (1988) The Kirbyville
Eucrite (Meteoritics 23, 1988, 382):

"Trace quantities of chromite and a few extremely
small grains of metallic Fe, Ni are found."


Best wishes,

Bernd
Received on Fri 18 May 2001 05:39:51 PM PDT