IMCA Insights – January 2012
The final scene of the
Morasko episode shows Geoff Notkin and Steve Arnold loading their
precious find into their car. A happy ending?
The 34 kg Morasko
weathered iron found by Steve Arnold.
It is well
known that scientists owe many of their meteorites used for research to
private meteorite hunters. Sadly, it is known that many meteorites do
not come with all of the potentially valuable information related to
their discovery and subsequent handling: type of soil where found, depth
of discovery, if and how it was cleaned, etc. I guess if the Meteorite
Men could have taken their find with them, it would have been cleaned,
cut and etched for display and sale. Some important information might
have been lost to scientific research.
minerals after removing an endpiece from the
It seemed to me that the find was not very weathered, so I started with chipping out the clay to uncover the iron metal. Surprisingly, a quite large endpiece came out, uncovering a dark, wet substance with elongated shiny inclusions. I tried on another side, where the darker surface suggested an iron oxide on metal. Instead, I uncovered a gray mineral with rather good cleavage and no metal again. So I decided to cut an endpiece off, to see, how deep the weathering went into the meteorite and how much metal was left inside.
Etched cross section
of the 34 kg find. There are many cohenite
It can be seen that some areas are much more affected by weathering than others. To the right of center, one can see a sharp border between metal and, cemented with brown iron hydroxides, clay. The same may be seen on the opposite side. But slightly lower on the right side and higher on the left side weathering went deeper into the meteorite, turning kamacite into black iron hydroxide and leaving only cohenite on the right side.
A microdruse of
chukanovite in the 34 kg Morasko iron.
The gray mineral with good cleavage mentioned earlier turned out to be the greatest discovery in the iron. It is a simple, but rare hydroxide-carbonate mineral of iron, unstable under normal atmospheric conditions. It was first discovered in the Dronino iron and named chukanovite in honor of the well-known Russian mineralogist. Morasko is the second meteorite in which this mineral was found. And this discovery would not have been possible if the find had been normally cleaned for collectors who would have removed all of the rust shell as a waste material.
A half specimen of
544 g Morasko shrapnel.
During filming I was kept aside so as not to be seen by the camera. But earlier, during scouting before filming, I had the privilege to be Geoff’s partner in hunting and I was lucky enough to find another Morasko specimen totally different from the big one. Steve’s find was individual, found deep in clay and strongly weathered. My find was shrapnel found at a shallow depth among stones and gravel and only weakly weathered. Both finds together are evidence that weathering grade tells us more about conditions in the ground than about terrestrial age, which is obviously the same for both finds.
Digging out the 34 kg Morasko iron.
finds are strewn very densely in a relatively small area on the northern
slope of a terminal moraine left after the last glaciation. This gave
reason for a supposition, that the iron could shower on a glacier and
then be deposited on the moraine. However, the large iron was found
embedded in the 2 million year old colorful Poznań clay, which means it
had to penetrate the soil instead of being deposited. Unfortunately, the
tight schedule of filming and poor weather left no time for examining
the excavation in search of traces of a hole made by the iron
penetrating the ground.
This article has been compiled and edited by Anne Black and Norbert Classen