[meteorite-list] Ringwoodite in my 3.22 gr Beni M'hira impact melt slice?

From: Bernd V. Pauli <bernd.pauli_at_meteoritecentral.com>
Date: Sun, 18 Aug 2013 19:28:35 +0000
Message-ID: <DIIE.0000004D0000677A_at_10.0.100.101>

Hello List,

Two of my six Beni M'hira (L6; S5; W0) specimens exhibit severely
shock-melted areas. When I first saw the 3.22 gr slice, a pitchblack,
charcoal-like melt "channel" flow within a shock-melted area instantly
caught my eye and prompted me to purchase it immediately.

Under the microscope (magnification: 16x), this "channel" is not jetblack
at all but displays instead a bluish tint. I have a hunch that this might be
ringwoodite.

Ringwoodite occurs in L6 chondrites of shock stage S4-S6. For ringwoodite
to form it takes shock waves exceeding 50 GPa. My two shock-melted Beni
M'hira slices look a lot like having experienced such a scenario.

Has anyone else observed such bluish areas in their shock-melted specimens
of Beni M'hira?

According to Lingemann ringwoodite occurs "as polycrystalline aggregates
of submicroscopic crystals replacing olivine grains inside or at the contact
to shock-produced melt..."

and:

"The color of the ringwoodite aggregates ranges from purple to blue and colorless."

Reference: Lingemann C.M. et al. (1994) Ringwoodite in shocked chondrites
(abs. Meteoritics 29, 491-492).

Best wishes,

Bernd
Received on Sun 18 Aug 2013 03:28:35 PM PDT