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815.7 gram slice.   Iron, IIAB

TKW 100 kilograms. Fall not observed. Found in Morocco, in 2000.

 

Steve writes:

The first pieces of Agoudal – also known by the provisional name Imilchil – were found in Morocco’s High Atlas Mountains in 2000, where roads from the Todra and Dadès valleys merge. Two of the first pieces from the fall were subsequently sold to tourists as non-descript minerals. But in September 2011, a dealer in Er-Rich purchased a piece and recognized it as an actual meteorite. It has since been classified as a type IIAB iron.

Later geological studies at the impact site identified a 600-meter diameter crater that was two-thirds covered by a 220-meter long, 40-meter thick limestone block, suggesting a landslide had occurred sometime after the meteorite’s fall. It’s presumed this block helped protect the crater from erosion over the estimated 40,000 years since the original meteorite impact.

Agoudal exploded into thousands of pieces during its descent, creating an 11 km by 3 km strewn field located near its namesake town of Agoudal – one of the highest towns in Morocco. Despite a 2300-meter elevation that makes searching especially hard, meteorite hunters began flocking to the site in 2012. Since then, hundreds of 1- to 10-gram samples, and several in the 100- to 1000-gram range, have been found. Besides some additional few-kilogram specimens discovered 30 to 50 cm below the surface, single 20, 23, and 60 kg individuals were also found. Later, an approximately 100 kg piece was recovered from a depth of about 2.5 meters, making the TKW well over the 100 kg listed in Agoudal’s 2013 MetBul entry.

Some examples of the meteorite exhibit flow lines, small regmaglypts, and even signs of orientation. Larger pieces yield some exceptionally nice slices and also show interesting alloy inclusions, Neumann lines, and in rare cases, signs of recrystallization from massive collisions in the asteroid belt.

Shatter cones – terrestrial rocks having curved fractures with diverging striations created by strong shock waves from meteoritic impacts – as well as suevite and other impact material, were also discovered in 2012 within the strewn field, making it Morocco’s first known site with impact evidence. Mapping of these shatter cones suggested an impact structure existed before the fall that created the meteorite fragments, which if true indicates there were two significant events at this spot: a first one that created the large impact feature and scattered shatter cones over an area consistent with a structure at least 3 km wide; followed by a more recent one that left the meteorite fragments found scattered around the strewn field.

Some researchers, assuming a relatively constant erosion rate over time, suggest that first event would have had to occur at least one million years ago to erode the 3 km impact structure to today’s 600-meter crater – an age possibly long enough to have weathered away any remains from that fall, as no remnant individuals have been discovered mixed with the fragments from the more recent event. Conversely, the meteor associated with the Agoudal fall likely broke into hundreds of fragments as it entered the atmosphere, which slowed from atmospheric friction to a velocity that was not fast enough to form a crater or create the observed shatter cones.

But other scientists discount this dual impact theory, not just because of its statistical unlikelihood, but also due to iron meteorite contamination in the shatter cones and meteorite fragments found in some impact breccia, both having the same chemical composition as the Agoudal meteorite. However, attempts to date the crater and material around it have not resulted in consistent numbers, so more work will be necessary to address this controversy.

Today’s post features a 815.7 gram slice from a larger Agoudal individual. Photo 1 shows both sides along with a ruler to give an idea of its size. Photo 2 and Photo 3 were taken outside to give a better idea of what the slice looks like in natural light. As seen in Photo 4, illumination makes a significant difference in the meteorite’s appearance – this photo was taken at a glancing angle as I was getting ready take some photographs under the microscope (compared to Photo 1 – the same surface, though rotated 180 degrees – the appearance looks considerably different).

This particular slice displays several interesting inclusions. Photo 5 shows a large one that can be seen on both sides of the slice. Photo 6 offers lower and higher power magnified views of what I presume are some kind of silicates. The remaining photos are animated GIFs taken with various changing lighting to better highlight some of the features. Photo 7 shows thin schreibersite rods sometimes referred to as rhabdite. The blotchy area shown in Photo 8 is seen in several areas across the slice and may be an example of recrystallization (its appearance is less affected by lighting than the schreibersite seen in the same photo). Photo 9 shows a multi-alloy metal inclusion. And Photo 10 offers an example of an oblong carbon feature is ringed by schreibersite.