Layered Chondrules in Allende CV3

These photos were taken of four thin sections that were deaccessioned by a US university. They appear to have been made by different people and at different times. On one, the cover slip cement has turned yellow. Some have labeling engraved on the slide behind the sample. Some of this can be attributed to the sample size being very large, covering most of the slide. Some samples have been polished a bit thinner than the standard 0.03mm. This might have been intentional since it helps reveal structures that are otherwise obscured by the fine grained matrix of this type 3 carbonaceous chondrite.

The layers in these chondrules distinguish themselves by differences in texture and composition. And these result from successive episodes of accretion and heating. Layers tend to be finer grained toward the outside of chondrules. We see different types of cores.

Core is a single crystal of olivine.

This is the same view as the photo above. The polarizing filters have been rotated putting the core grain into optical extinction to highlight its halo of fine grained material.

Coarse core surrounded by finer mineral grains.

Another single crystal core.

A barred olivine chondrule core with an untidy fine grained surround.

Two barred olivine chondrules and a layered chondrule.

Both chondrules have barred olivine chondrule cores. In the upper chondrule the bars are blue and red.

A jumble of bars is at the center of the chondrule surrounded by medium size grains and, toward the edge, layers of opaque material.

The black circles and curved traces are metal. They show better in the reflected light photo below.

The metal blebs and mineral grains in the center were surrounded by two metal shells before the chondrule was sliced open for inspection.

A 5mm diameter porphyritic pyroxene chondrule (with poikilitic texture) is surrounded by dark and finely crystalline layers.

Coarse center with finer surrounding layers. Some mineral grains were plucked from the center of the chondrule during thin section preparation.

0.66mm wide layered chondrule.

The outer layer is a barred chondrule so we know that part was fully molten at some time. When it solidified its internal crystal lattice grew in alignment with the adjacent core crystal.

About the Author

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