[meteorite-list] Purple (or bluish green) in a (stone) meteorite - ringwoodite

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Sun Oct 2 11:49:23 2005
Message-ID: <DIIE.0000003000003D80_at_paulinet.de>

Hello Harald and List,

.. and thanks for the reference!

www.lpi.usra.edu/meetings/lpsc2002/pdf/1264.pdf

> was also found in LL6 chondrites - especially in NWA 757.

Here are some other candidates in which ringwoodite has been found:

Umbarger L3-6 S6; mask.; sv; rw; shock-melted plagioclase; stishovite
SaU 151 L4/5 S6; W1; m.v., rw, mask
SaU 140 L4/5 S6; W1; im; rw
Acfer 040 L5-6 S6; W2; br; rw
Acfer 072 L5/6 S6; W2; br; sv; rw

Although not all of them are L6 chondrites, they are all severely shocked (S6).
Of these, as you can see, Umbarger is the most interesting one because of its
L3-6 classification. Not only does it have ringwoodite (the high pressure
polymorph of olivine), but it also contains maskelynite (plagioclase feldspar
transformed by intense shock pressure), and stishovite - the high-pressure
SiO2 polymorph. The occurrence of stishovite is consistent with a shock
pressure of about 18 GPa, and thus some parts of Umbarger were found to
be less intensely shocked (S4), still indicative of strong shock pressure
though!

There are several thick, black shock veins meandering through my Umbarger thin
section at 32x magnification and a large (1 mm) bluish-green, squarish pyroxene
crystal (pigeonite?) which looks awesome under 56x magnification because it is
cut (or split) into two halves by a shock vein measuring 0.06 millimeters across.


Cheers,

Bernd
Received on Sun 02 Oct 2005 11:49:21 AM PDT