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NWA 12692 LL3.00 S3 W2

The 3.00 designation is assigned to chondrites that have experienced the least amount of metamorphism. Few are recognized. In September 2021 there are ten. The two L3.00 are possibly paired.

NWA 8576 LL3.00 59.5 g
NWA 10061 LL3.00 53.8 g
NWA 12692 LL3.00 373 g
Semarkona LL3.00 691 g

NWA 7731 L3.00 81 g
NWA 8276 L3.00 789 g

Chwichiya 002 C3.00-ung 779 g
NWA 11750 C3.00-ung 8.5 g
NWA 12957 C3.00-ung 43 g
NWA 13689 C3.00-ung 165 g

NWA 12692 was found in Mali in 2012. They were sixteen stones having no fusion crust and weighing 2 grams to 157 grams. Classification was done by C. Agee at University of New Mexico Albuquerque in 2019. Material is on deposit there and at the Research Center for Astronomy and Earth Sciences, Budapest, Hungary.

The main mass is held by Z. Kereszty and it is from him that I bought the beautiful slice which I had thin sectioned. Z. Kereszty photo.

 

 

Chondrules are somewhat irregular and are densely packed. The matrix is black. The largest chondrule in this section is 3 mm across. Weathering grade is 2. A small crack extends from near the center bottom of the sample upwardly. It contains terrestrial weathering deposits. Thin section in transmitted light.

 

 

The rim on the fine grained radial pyroxene chondrule in the center is the result of hydrous alteration on the parent body. Field of view (FOV) is 3 mm. Plane polarized light (PPL).

 

 

Chondrules and mineral grains throughout have been stained by terrestrial weathering. PPL and oblique incident light.

 

 

Center chondrule appears to be embracing something. FOV=3 mm, PPL.

 

 

Something granular. PPL and oblique incident light.

 

 

But not bright enough to be metal. Much more detail shows in otherwise opaque areas. Reflected light.

 

 

Larger chondrule with granular and dark appearing inclusions. FOV=3 mm, PPL and oblique incident light.

 

 

The otherwise dark inclusions appear bright like metal. Reflected light.

 

 

Chondrule with dark spot surrounded by opaque material. FOV=3 mm, PPL.

 

 

PPL and oblique incident light.

 

 

Chondrule appears to be surrounded by metal – armored. Reflected light.

 

 

Textured metal.

 

 

Chondrule with a few dark spots. White areas are where material was lost during the thin section making process – “plucked grains.” FOV=3 mm, PPL.

 

 

Dark spot at 2 o’clock looks fuzzy. PPL and oblique incident light.

 

 

In cross-polarized light (PPL) that spot looks like it might be a relict grain.

 

 

A closer view finds that it has the typical “dusty” appearance of a relict grain.

 

 

An 8 mm wide field hinting at the variety of chondrule types and sizes. The bright one in the center looks interesting. XPL.

 

 

Same chondrule in center of a 3 mm wide view. XPL.

 

 

Chondrule has a fine grained texture. It is 0.4 mm long. XPL.

 

 

The largest chondrule in this thin section is an irregular 3 mm in diameter. The vaguely radiating appearance is reinforced by sequential optical extinction between rotating crossed polarizing filters.
John Kashuba

John Kashuba

John is a natural history enthusiast living in Oregon.
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