[meteorite-list] Iron Breccia

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:59 2004
Message-ID: <3C5B0B85.3443668A_at_lehrer1.rz.uni-karlsruhe.de>

Matt Morgan asked:

> Isn't Willamette recrystallized, not brecciated?

after Rick had written:

> Another candidate could be the Willamette on Darryl's auction page.


Hello Again,

Wow, what a beauty, this Willamette (#13) on Darryl's auction page!
There are several b&w pictures in Buchwald's trilogy but that color
pic is breathtaking!

Well, Matt to put it in proper perspective, let me quote Buchwald's
comment once again:

BUCHWALD V.F. (1975) Handbook of Iron Meteorites, Volume 1, pp. 69-70:

A number of irons were previously termed "b r e c c i a t e d"...The
term is unfortunate and should be abandoned. The meteorites are not
brecciated in the geological sense but are polycrystalline aggregates
of ferrite or austenite grains ... Holland's Store, ... probably
acquired its peculiar structure by recrystallization of a shock-deformed
single kamacite crystal.

Buchwald quite intentionally avoids the term "brecciated" and does not
use it anywhere in his description of the Willamette iron. Instead, as
you correctly stated, he constantly uses the term "recrystallized".

As for its complicated structure, he envisions this series of events:

Stage 1: Primary slow cooling period resulting in a medium Widmanstätten
             structure
Stage 2: Significant shock + subsequent reheating with kamacite
             recrystallization
Stage 3: Another less intense shock event creating Neumann bands in the
             recrystallized kamacite
Stage 4: Penetration of the atmosphere
Stage 5: Final long-term exposure to humid Oregon climate with formation
             of the deep cavities


Best wishes,

Bernd
Received on Fri 01 Feb 2002 04:41:25 PM PST