
An Article In Meteorite-Times
Magazine
by John Kashuba
Chuck,
Let me point out another place
to see good thin section pictures. Jeff Hodges has a great collection of slides
and a very good microscope. He loans thin sections to Tom Phillips (we talked
about Tom last time), particularly polished sections (no glass cover slip) that
Tom really likes working with. Jeff’s evolving site is:
http://meteoritethinsectiongallery.com/index.html
I just got a thin
section with a large variety of features. It is from a slice of NWA 4560 LL3.2.
Take a look.
- John


This is the slice the slide was made from,
front and back.
I don’t think any of either of the two obvious inclusions became
part of this particular slide.

Just for laughs, here is a different slice
of this same find. Pretty wild. Its grade of 3.2 tells us it didn’t get
a lot of
heating back on its home asteroid. But obviously it’s seen some mechanical
pushing and shoving.

This radial
pyroxene chondrule has been cratered and there is alteration around the edge.
Roger Warin and I have an article on cratered chondrules in the November 2009
issue of Meteorite magazine.
I hope you are a subscriber. We have pictures
and we touch on a few theories of how they came to be.

This fragment of a RP chondrule was
separated after alteration took place.

Similar story, lots of aqueous alteration
bleached the outside part of a RP chondrule before it broke and a fragment ended
up here.

Let’s have a vocabulary review:
Euhedral crystals are well-formed with sharp, easily-recognized faces.
Anhedral crystals lack sharp, recognizable crystal faces.
Subhedral – neither
fish nor fowl.

Here is a contrast in textures, fine
granular olivine on the left and coarse pyroxene on the right.

Okay. Nice Barred olivine chondrule with a
thin rim, but what’s happening there on the bottom?

Ah. Here it is in incident light. Like we
suspected, that black is a big bleb of metal.
And that other business around it
looks to be material accreted after the BO chondrule formed.

Hmmm. Cryptocrystalline interior and some
well crystallized portions on the outside?

A dusky interior. Maybe a relict grain – a
crystal fragment that did not (re)melt when this chondrule formed?

This dark amorphous inclusion is 6 mm
long. The metal has been melted but the mineral fragments are angular.

Finally, another set of contrasting textures including a pair of wispy, poorly
crystallized fans and a couple variations on the barred olivine theme.