FMF - Friends of Minerals Forum, discussion and message board

[Tomsalwayssmilin]

I found this rock a few years ago on the edge of a collapsing hillside in NW North Dakota. It's about a foot long and about 9 inches across. Slightly smaller than a bowling ball. It weighs around 10 pounds.

I've contemplated breaking it in half, but if it's going to just be a solid piece of sandstone I'd rather just leave it as is. What do y'all think about it? It's quite interesting to say the least.

[SteveB]

looks like someone poured concrete into one of those speed ball punch bags. The shape, the seams its all there.

[Tomsalwayssmilin]

Lmao now that you pointed that out it really does look like that. My wife said it looks like a skull. It's definitely not concrete though. I'm almost 100% positive it's sandstone. We have it all over up here and where I found it there were giant pieces of sandstone all over.

[Bob Harman]

Identifying rocks only from photos is quite difficult and we prefer minerals to rocks on this website. However blowing up your second photo and scanning the whole surface, I see small remaining areas where crinoid stems and/or archimedes or similar pieces once were.

I believe you have a rounded large cobble of limestone or silicified limestone containing remaining bits of invertebrate fossils. If it is limestone, it will fizz when placed in muriatic acid (28% HCl) for a minute or two. If it has become silicified, that is replaced by quartz, little or no fizzing will occur, but still that is what you have. BOB

[Tomsalwayssmilin]

Thank you for your response. A lot of the people I had shown it to after I found it thought it was a geode so that's why I thought this may be a good place to ask about it.

I may have to get some muriatic acid and see if it fizzes at all. Thank you for the suggestion.

[Joseph DOliveira]

I agree with Bob, it looks like a piece of limestone. The orbicle shape and grooves give the appearance that the stone was worked. It may be possible that you have a native artifact of some kind.

[Tomsalwayssmilin]

Thanks for your reply Joseph. I never thought about it being a possible artifact before, but that's also a very good possibility.

[Mathias]

This looks typically like a rock containing an ammonite fossil inside.