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Met Name

Met Type

Thin Sections

  Iron, IIC

TKW 80kg. Fall not observed. Found 1920, Unter-Mässing, Germany.




   

jnmczurich writes:

The iron meteorite Unter-Mässing (U-M) was unexpectedly found in 1920 during excavation work near the junction of Röckenhofen and Oesterberg at a depth of about 1.5 m. U-M is still the largest meteorite ever found in Germany.

Pic 1 – U-M almost complete mass, on display in Natural History Museum of Nuremberg/Germany

U-M is structurally classified as IIC iron, plessite octahedrite (Opl) with 0.06 mm narrow kamacite spindles and is one of only eight meteorites worldwide with this IIC classification. The structure of U-M consists essentially of two phases, Ni-poor kamacite and Ni-rich taenite. Schreibersite (FeNi)3P (chemically Schreibersite is an iron-nickel phosphide) and troilite FeS (iron sulfide in stoichiometric equilibrium) are included in U-M as inclusions.

Since there were enough b/w micrographs of U-M iron known from the meteorite literature, the sample was carefully prepared for color etching by using Klemm-1 etching solution.

Please note: micrographs of a color-etched U-M sample are a novelty and have not yet been reported from any other source. However, most of the images shown here were presented to a small group of colloquium participants at the two years delayed (Corona restrictions…) German Meteorite Colloquium on the 100th anniversary of finding the U-M Iron, in August 2022.

Pic 2 and Pic 3 – polished U-M partial slice and the same U-M partial slice in color-etched condition. The red marked fields are showing the investigation fields - see following pictures. The black strips in the overview picture are cracks that are partially filled with Schreibersite. U-M is a cosmically strongly shocked iron meteorite.

Pic 4 – to guide you though the micro-photography images, please see investigation field 4 in Pic 2. Color etched U-M with 25 times magnification. Scale 500 µm.

Pic 5 – color etched U-M with 100 times magnification. Scale 100 µm. Blocky or worm-like white/cream-colored, cracked schreibersite inclusions (S). Cracks in the schreibersite are caused by strong shock. Blue/light blue colored Ni-poor kamacite (K). White, thin taenite bands (T) border the blue/light blue/grey/light grey kamacite fields. Brown areas finely speckled/streaked with blue are plessite (P).

Pic 6 – color etched U-M with 25 times magnification. Scale 500 µm. Striking, vertically directed schreibersite inclusion. In the image is seen a slight efflorescence (discoloration) caused by the etching agent sitting deep in the cracks.

Pic 7 – color etched U-M with 100 times magnification. Scale 100 µm. Horizontally directed schreibersite inclusion, enveloped by kamacite (grey in various shades), with narrow taenite bands delimited from the plessitic matrix.

Pic 8 – color etched U-M with 100 times magnification. Scale 100 µm. Torn inclusion of schreibersite (white) as a probable consequence of a strong shock situation. Brown areas finely speckled/streaked with blue are plessite.

Pic 9 – color etched U-M with 100 times magnification. Scale 100 µm. Blocky schreibersite inclusions, streaked with cracks (white) in the middle of kamacite spindles (blue/grey). The kamacite spindles are bordered by a thin white rim of taenite banding towards the plessitic matrix.

Pic 10 – color etched U-M with 100 times magnification. Scale 100 µm. Several elongated kamacite spindles (various blue colors). Blocky schreibersite inclusions with cracks in the kamacite spindles. Fine blue/brown colored plessitic matrix.

Pic 11 and 12 – color etched U-M with 500 times magnification. Scale 20 µm. Two pictures in higher magnification as a bonus to enjoy…