[meteorite-list] Olivine with Spinel Structure in Meteorites

From: Sara Russell <sarr_at_meteoritecentral.com>
Date: Thu Apr 22 09:46:22 2004
Message-ID: <E14wkO4-0001M4-00_at_pat.nhm.ac.uk>

Dear Elton and list

Although ringwoodite requires high pressures to form, its presence does not
necessarily indicate it came from a big parent body. On Earth, it is
predicted to exist because of the high pressures caused by the large mass of
Earth. However in meteorites, ringwoodite forms by a different mechanism- it
is always associated with shock features, and so it is thought to form in
the high pressures experienced by a collision between two asteroids- a big
parent body is not required, only very high collisional velocities.

Also, while perovskite is often associated with high pressure mineralogy in
many terrestrial samples, in meteorites perovskite is most abundant in
calcium-aluminium-rich inclusions, and is thought to form at very high
temperatures, but low pressures, in the solar nebula. Its formation is not
linked to ringwoodite.

hope this helps

Sara

*************************************
Dr Sara Russell,
Department of Mineralogy,
The Natural History Museum,
Cromwell Road,
London,
SW7 5BD, U.K.

Tel: +44 (0) 20 7942 5074
Fax: +44 (0) 20 7942 5537
Received on Mon 07 May 2001 08:45:16 AM PDT