What is this?
I found a very unusual rock last fall that I have some trouble identifying. Since this being Sweden the damn glaciers of the Ice age transport rocks all over the place (or at least from the north to the south). So the provenance of the stone is basically unkown except that it must be something possible for Sweden and neighbouring countries. I have never seen anything like it here in Sweden but perhaps some of my english speaking readers out there have at least a qualified guess to offer me. It doesnt look like any sedimentary rock that Ive seen anywhere in Sweden before. I have my guess of course, but I want your oppinion on it.
As you can se from the images its some sort of sedimentary rock. It basically looks like some form of clay (or silt) stone with stripes of quarts sand in it and rich in Iron (but that could of course be something it was exposed to simply). I havent actually weighed it, but it feels quite heavy, perhaps because of the iron?. The larger granule/grain in the middle is also quartz as far as I can tell.
Update: Added two more closeups.
January 18, 2009 + Posted in Mineralogy, Petrology, Sweden +
It has some crude bedding to it … and there are parts that look like they have a bit of soft-sediment deformation (i.e., bits and blobs of sand stringers ‘floating’ in the finer-grained matrix).
There’s no ’smoking gun’ diagnostic feature that I can see in these photos to help pinpoint a process interpretation. If one really wanted to know, they could thin section the finer-grained parts to see if there is any very subtle variations in grain size vertically. It would be nice to know if the finer-grained part is homogenous, or does it have any grading? Any very fine structure?
At this point I’d be hard-pressed to guess at an origin for this rock … need to ponder a bit more. Maybe others have offer some good insights.
Comment by BrianR — January 18, 2009 @ 7:13 pm
Brian: Theres no grading what I can see in the matrix on close inspection. It seems solid. Ive added two more photos.
Comment by Antimonite — January 18, 2009 @ 7:50 pm
I think the heaviness has got to be from the contained iron. The rock reminds me of ferricrete - but that is mostly the color; they do not usually consist of mudstones or siltstones. The only part of it that looks at all fragmental like a ferricret is in the top photo near the top of the rock, where the disruption is probably wavy bedding. But it does make me wonder if Fe-rich solutions from a nearby (or palaeo) spring didn’t seep through this mudstone. I can’t add much of anything to the origin of the rock other than it looks sedimentary, and is pretty neat looking! Would be great to find The Source!
Comment by Silver Fox — January 20, 2009 @ 3:58 am
Silver Fox: Thanks for your input.
Comment by Antimonite — January 21, 2009 @ 12:18 pm
It looks rather like the various limonite & other concretions/zones that I’ve seen in the New Jersey & Maryland Coastal Plain Cretaceous units.
Comment by mark — February 13, 2009 @ 9:25 pm
http://www.geolsba.dk/echinoids/listeCampan.html
Comment by personnic — November 26, 2009 @ 8:29 am