[meteorite-list] planar fractures?

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Fri Feb 4 16:08:57 2005
Message-ID: <DIIE.0000003100003226_at_paulinet.de>

Tom wrote:

> Hello List, can anyone explain planar fractures in meteorites
> to me? I have been reading about them, but I can't seem to
> find a simple explanation.

Hello Tom and List,

If meteorites suffer intense shock pressures (at least shock stage S3), their
minerals, especially olivine crystals, will break parallel to their crystal
faces (or planes, hence "planar"). These cracks or fractures can be easily
observed in thin sections under a microscope as a set of parallel lines or
as a set of crisscrossing lines (in the olivine crystals).

I will send you a thin section JPEG of planar fractures in an olivine crystal
in my Travis (a) thin section. It shows an intersecting set of planar fractures
(along with opaque material). This H5 chondrite is even shock stage S4 and has
a shock-blackened matrix.

I have marked two crystals (one yellow, one blue in crossed polarized light)
in the centre of the field with arrows where planar fracturing is particularly
noticeable.

I also have a gorgeous 40-gram slice of this beautiful chondrite with
a shock-darkened matrix that I got from Michael Cottingham some time ago.


Best wishes,

Bernd
Received on Fri 04 Feb 2005 04:08:56 PM PST