[meteorite-list] Ibitira in thin section

[Gerald Flaherty]

Marvelous description Bernd. Readable textbook!! I've printed it out as a 
keeper. I'll try to apply it to other thin sections down the road. It  is, 
after all, much more fun to be able to identify the characters responsible 
for the OOH's and AHH's in any wintessed "drama" !!
Jerry Flaherty
----- Original Message ----- 
From: <bernd.pauli at paulinet.de>
To: <Meteorite-list at meteoritecentral.com>
Sent: Saturday, March 19, 2005 4:41 PM
Subject: [meteorite-list] Ibitira in thin section


> Hello Listees, Listoids, List,
>
> The noncumulate, unbrecciated, monomict Ibitira eucrite with its
> mm-sized gas holes or vesicles has always been on my wish list
> (see O.R. Norton, p. 153 Cambridge Encyclopedia of Meteorites
> for a breathtaking slice measuring about 10 by 10 cm in size).
>
> So I was more than happy when Michael Cottingham offered a small
> but very characteristic slice of 0.21 grams for sale some time ago
> that I immediately purchased from him.
>
> Not long ago, Michael Blood offered 3 Ibitira thin sections, one of
> which I acquired, as this would be the ideal complement to my little
> slice and it even looked so similar -- almost as if it had been cut
> from the same piece.
>
> Today, when I looked at my Ibitira thin section under crossed polars and
> with several different magnifications, there were many "oohs" and "aahs"
> at the spectacular, colorful Ca-poor pyroxenes (pigeonite) most of which
> are crossed by countless parallel, fine laths of Ca-rich augite (so-called
> exsolution lamellae).
>
> The pyroxenes account for about 60% of my thin section, the second most
> abundant phase is, of course, plagioclase (grayish-white because it is
> chemically zoned). These plagioclase crystals show undulatory extinction
> when you rotate the section under your microscope with polars crossed.
>
> There are also several opaque inclusions throughout the section (they look
> black both in transmitted light and under crossed polars). According to 
> the
> literature, they are ilmenite (CaTiO3), chromite (FeCr2O4), FeNi-metal and
> troilite.
>
> Ibitira is also said to contain the silica polymorph tridymite (SiO2) but 
> I
> haven't been able to locate these laths yet as I've never looked for 
> tridymite
> before. These laths can be as long as 7 mm (in NWA 1181) but are usually
> about 1 mm in length.
>
>
> Best Eucritic
> Wishes,
>
> Bernd
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list