NWA 4560 LL3.2

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.

Tags:

About the Author

John Kashuba
John is a natural history enthusiast living in Oregon.
Top