[meteorite-list] Diogenite Distinctions....was List of meteorites from Vesta?

From: MEM <mstreman53_at_meteoritecentral.com>
Date: Thu, 7 Apr 2011 03:09:53 -0700 (PDT)
Message-ID: <999525.1912.qm_at_web161909.mail.bf1.yahoo.com>

<<Dunite is the "Earth version" of Tatahouine.>>

Sorry, well.... but not exactly. Orthopyroxene is close elementally but
chemically a different class of silicate mineral. Pyroxene isn't the same as
dunite--aka olivine rock. There is an axiom in mineralogy :" color is the list
reliable characteristic for identification". Pyroxene forms when the available
oxygen is less than optimal (as in Olivine)so it has to stack differently to
double up on oxygen bonds.

How-so-ever, there is at least one NWA achondrite described as "Dunite with HED
affinities" yet the same literature keeps talking about "olivine diogenites".
What level of olivine content switches from Olivine Dio over to a Dunite Dio?

Perhaps the use of "dunite" in the literature is more inline with the trend to
describe achondrites in terms of rock-type/rock fabric, than traditional
composition-based schemes. Remember the old days of Olivine, Bronzites, and
Amphoterites instead of H, L and LL?

Elton
Received on Thu 07 Apr 2011 06:09:53 AM PDT