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An MPOD Classic from from 12 August 2014

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Thin Sections

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Allende   contributed by John Kashuba   MetBul Link

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View all entries for   Meteorite (51)   John Kashuba (9)

What is a thin section?       What do all the colors mean?    

TKW 2 tons. Observed fall 8 February 1969, at the village of Pueblito de Allende, Chihuahua, Mexico.

John writes:
This animation cycles through four images. They are photos of a portion of a thin section of the Allende CV3 meteorite under a microscope in cross-polarized light, XPL. The orientation of the crossed polarizing filters was different for each picture. The subject is a barred olivine, BO, chondrule with an hourglass configuration.

Simple BO chondrules are single skeletal crystals in the form of parallel plates of olivine enclosed by and connected to a spherical shell of olivine. The plates are separated by feldspathic glass. In thin section and viewed in XPL simple BO chondrules are uniform in color and go to extinction - black out - all at once as the polarizing filters are rotated relative to the slide. The hourglass chondrule has two colors and those domains differ in when they go to extinction. Clearly, these are different crystal domains yet related. Research has shown that hourglass barred olivine chondrules are crystallographic twins.
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Jesper Grønne

This Month

 8/13/2018 11:55:32 AM
Nicely presented! Is there any recent information which provides conclusive evidence as to how these condrules were formed?
 8/12/2018 2:52:03 PM
Very nice John great job! Regards, Joe IMCA #7960
Anne Black
 8/12/2018 1:53:32 PM
I have seen this picture many times, and I still find it amazing. Thanks John!
Bernd Pauli
 8/12/2018 6:22:40 AM
Interesting animation! Beautiful hourglass BO chondrule + sibling BO chondrule ... both with an igneous rim. Thanks for sharing, John!

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