[meteorite-list] More petrographic questions.

From: Robert Beauford <wendirob_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:08 2004
Message-ID: <003b01c092fe$f9301400$804897cc_at_wendirob>

Petrographic grade 7 (on a scale of 1-6) means that the chondrules are
completely obliterated. This is a transitional type to achondrites.
Question: When, specifically, is this grade used, and what makes it a
Chondrite of petrologic grade 7 instead of an achondrite?

Petrologic grade 3 chondrites are subdivided by thermoluminescent analysis
based on feldspar crystal development distinguishing slight differences in
metamorpic alteration (ie: alteration by heat) that are not great enough to
make them a grade 4.
Question: Based on this analysis, how have the grade 3's distributed
themselves? (What is the most common subtype and how common are the others?
Is it a uniform decrease in frequency of types as one goes from a grade 4
down to a grade 3.0? Are there any 3.0's?

What is the process of formation and early history of chondrules prior to
accretion in larger bodies?

Again, any insights that you are willing to take the time to share will be
greatly appreciated.
-Robert Beauford : )
Received on Fri 09 Feb 2001 08:15:08 PM PST