[meteorite-list] NWA 1109 Howardite or Eucrite?

From: David Weir <dgweir_at_meteoritecentral.com>
Date: Thu Apr 22 10:07:00 2004
Message-ID: <3DA81884.73D314A4_at_earthlink.net>

Hello Frank and list,

fcressy wrote:
> The rock is a howardite if it contains greater than 10%
> orthopyroxene and a polymict eucrite if it has less than 10%.

Frank I don't believe this interpretation of the rule is correct. From
what I gather, a polymict eucrite contains more than 90% eucrite
components, but the remaining 10% may consist of anything else,
including a small, less than 10%, component of orthopyroxene, together
with a small, perhaps 5%, component of your dark material along with
accessory minerals.

However, given the specific composition you proposed ...
"hypothetically, if NWA 1109 has an orthopyroxene (diogenite) component
of 8% plus another 5% of chondritic material" ... then I would say it
would be a howardite because it is inconsistent with the definition of a
polymict eucrite or diogenite, which specifies that it must contain
greater than 90% of a single component, and that would be impossible
since 12% is accounted for.

I would also imagine the case could arise where part of a meteorite is a
howardite and part is a polymict eucrite. I would think that the
additional method of distinguishing them apart, zoned versus unzoned
pyroxenes in basaltic clasts, would be helpful in this case.

David
Received on Sat 12 Oct 2002 08:41:40 AM PDT