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Ozerki L6 IMB

Ozerki fell June 21, 2018 in Lipetsk oblast, European Russia, about 240 miles south of Moscow. More than a hundred stones were found totaling over 10kg. It is an L6 ordinary chondrite.

Various shock levels are reported. The stone from which our thin section was made has been strongly shocked. It is a breccia of L6 clasts within solidified melt. Mineral grains exhibit undulatory extinction.

Metal and sulfides were mobilized by shock and are present as crosscutting veins, opaque blebs within the melt and injected between minerals and in cracks in mineral grains. In reflected light the opaque drops in the melt and some within the L6 material have a distinctive metal-troilite intergrowth texture.

The melt rock matrix is translucent in thin section, unlike many meteorites whose melt is opaque and some whose melt is glassy transparent. The Ozerki melt devitrified into micro crystals, presumably during a somewhat extended cooling. Microscopic acicular crystals are massed at some depth on the surface of the intact L6 clasts generally parallel with each other and perpendicular to the surface of the clasts.

One patch of another melt, some remnant fusion crust, also had time to form a crystalline layer – beneath a glassy vesiculated exterior. I believe that, in one spot there, we have an instance of epitaxy.

 

The sample is about 22mm wide. Thin section in transmitted light.

 

 

As expected in an L6, there are few identifiable chondrules. The two we found are rather large.

 

 

Transmitted cross-polarized light.

 

 

Both chondrules contain bars. Field of view is 3mm wide. XPL.

 

 

Nearby, these orange bars might once have been part of a chondrule.

 

 

The bars actually appear better in optical extinction.

 

 

This wavy set of bars is frozen in a sea of melt and go through undulatory extinction as the polarizing filters are rotated. This indicates a moderate degree of shock.

 

 

We’ll look closer at this 4.4mm wide area.

 

 

L6 clasts surrounded by melt rock. The melt is devitrified and contains blebs of metal sulfide and mineral grains. If the melt was not crystalline it would be black, here in XPL. FOV=4.4mm.

 

 

The devitrified melt rock texture immediately surrounding these L6 clasts is different than that further away. Below is a closer view at the area at the bracket. PPL.

 

 

Acicular crystals grew from the surface of the L6 clast excluding and displacing opaques—rather like freezing water in grapes concentrates sugars for ice wine. Crystallization is a purifying process.

 

 

The same 0.5mm wide area in XPL.

 

 

Metal and troilite are bright in this reflected light view.

 

 

Metal-troilite spheres and veins in melt and L6 clasts. These are the black (opaque) objects in the center of the fourth photo above. Reflected light.

 

 

Intergrown metal-troilite. Half a millimeter long. Reflected light.

 

 

Finally, let’s examine a small bit of fusion crust. It is thicker than the crust on the top right.

 

 

The remnant is about a millimeter long and 0.3mm thick.

 

 

The fusion crust sits partially on solidified rock melt and partially on L6 material. The crust layer in contact with the stone has crystallized. The outer layer cooled fast to glass and contains voids, that is, bubbles.

 

 

It appears that the fusion crust melt that was in contact with the, here, yellow mineral grain crystallized in an orderly manner apparently linked with that mineral grain. I suggest this is epitaxy which is defined as the natural or artificial growth of crystals on a crystalline substrate determining their orientation. In semiconductor manufacturing crystalline films are grown on substrates that are often of the same material as that deposited (though without doping). Convention in the mineral world reserves the term “epitaxy” for such a relationship between different minerals. Some mineral examples follow.

 

 

Golden rutile epitaxially grown on black hematite. Even though they are not of the same crystal systems (rutile is tetragonal and hematite is trigonal), their crystal lattices have a way of aligning.

 

 

Cumengeite pyramids often grow very neatly on the faces of boleite cubes. This is not twinning.

 

 

Torbernite epitaxy on saleeite. Two uranium minerals. This specimen is from the Shinkolobwe mine, Democratic Republic of the Congo.

 

 

Until it is shown that the grain and overgrowth are the same mineral, I claim it’s epitaxy.
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