Iron Shale Memories
One of the meteorite related items that I have a lot of in my collection is iron shale from Barringer Meteorite Crater. I have many kilos of the stuff. To most collectors is is more or less a waste product. It is not a meteorite anymore it is what a meteorite turns into. Many will not have it in their collections unless it is the only remaining material for a meteorite. That is the case actually with several old craters. But I find the material quite fascinating. I have cut it and ground it up and tested it for nickel. I have lapped and polished many small pieces. I must have been about 14 when I cut and polished the first piece of Meteor Crater iron shale. It was one of the pieces I found there. There was nothing noticeable about it at first glance. It was just dark gray rock with a metallic luster. It looked like hematite but had a black streak not red. It was exactly like magnetite to me then and sort of pretty when polished. But looking at the piece more carefully revealed something that as a child I had not yet learned. There were tiny little specks of residual nickel-iron metal in the shale. Showing on the surface of the polished face as small brighter flecks, but only visible under a hand lens with the light angled just right.
As I was writing this article I tried to remember where I had read years ago about the residual metal in Canyon Diablo iron shale. I was pretty sure that it was a Nininger source. I skimmed through his book Arizona’s Meteorite Crater but did not find the reference. I have read the passage at least twice in my life. The first time I saw the statement was only shortly after cutting that first piece of shale as a kid. But, I can not remember now where the reference is from.
I have some remarkable pieces of shale in my collection. One chunk is over 900 grams and is layered in flat sheets with no curvatures at all. Other pieces like the one photographed below show much more of the character of the original meteorite fragment they were derived from. Some angling of the various blocks and a curvature across what is clearly the original outer surface. It is only a portion of a shale ball but still wonderful.
Specimen of Canyon Diablo iron shale. Weight 232 grams
Some pieces are very magnet responsive others are only very slightly responsive to a magnet. Another little experiment I did as a kid was to find one piece of shale that was very reactive to a magnet and see if it would align itself when suspended on a string to the Earth’s magnetic poles like a compass needle. And to my surprise it did. I still have that piece with the S and N I painted on it forty years ago.
I did not find any real meteorite fragments at the crater the first trip I took there. I would later. That first trip I did find a nice group of shale fragments. Later going through boxes of iron shale collected by others I would find some real meteorites mixed in that they had missed. Always fun to do that. But, one of my nicest moments near the crater concerning iron shale was finding about ten small pieces on the side of the Nininger Museum ruin just where the little dirt road goes past the west wall. I like to think and believe I am right that they are fragments brought by him decades ago to that spot where he unloaded some larger meteorite covered in shale.
There was once a tremendous amount of iron shale around the crater. Not much is visible today. It was an important feature to early investigators of the crater and remains one of the materials I love to work with.