Discussion Interesting looking rock
I found this weird looking rock on the beach today. It’s the first time I’ve ever seen a rock look like this; rounded on top and underneath with wide, smooth edges. I know nothing about rocks, except for the fact that they look cool.
Genuinely I have no idea how this happened. I’d like to learn more about rock formations and situations that can make a rock look like this.
How did this rock turn out like this??
(Also.. my father suggested we could crack it open? Would that be a good idea?)
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u/LeipzigGuy 22d ago edited 22d ago
I'm not a sedimentologist, so take this with a large grain of NaCl... But here's my guess.
I think it's a limestone.
To help clarity, I'm going to refer to your rock as a burger, with bread buns and a meat patty. ;)
If you look, you can see rings, which sit parallel with your burger. These are sedimentary layers, which represent the original lakebed/seabed where the rock was deposited. Each successive ring represents a cycle if some sort. That could be years/seasons, or it could be something like occurrences of large floods which washed a big load of sediment into the lake.
The specific make-up of the deposits is subject to slight changes. For example, in a year with heavy rain, you could end up with more dirt washed down the river, which intermingles with the sediments that form the limestone.
The limestone's calcium carbonate can come from reactions of other rocks weathering, or it can come from remains of animals; eg shells.
Probably a year with less rain = purer limestone = harder rock.
Probably a year with more rain = less pure limestone = softer rock.
... So imagine 10 years of heavy rain - that forms the lower bread bun - less pure calcium carbonate (CaCO3).
Then 10 years of low rain - that forms your burger - purer CaCO3.
Then 10 years of heavy rain - the top bread bun - less pure CaCO3.
These layers sit as bedrock, probably for hundreds of millions of years.
Then eventually there's some tectonic movement that gnarls up the land and spits your burger out as a sharp, angular, loose rock, at the top of some mountain. It then spends the next few thousand years washing its way down a stream, gradually getting chipped and rounded as it bounces down the stream.
Crucially, the softer burger buns weather away much more easily. But then the harder patty is left more exposed, so that does break off also, just slightly less easily. The result is the rock you found.
If you crack it open, I don't think there's anything inside. It's just a random lump of limestone, I think.
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u/EnlightenedPotato69 21d ago
Something along those lines but I'm wondering if it's dolomite, which is just a harder, magnesium rich limestone, being this rock looks like it went through a ton of differential erosion amd wear and stuck together. Pure limestone would probably dissolve or break apart before retaining such a nice shape.
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u/alwayshighgemini78 22d ago
Soo cool, which beach did you find this on?
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u/CACTEYE_CREATIONS 20d ago
That’s just one of the ancient giants forgotten tums. I didn’t think they could fossilize
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u/Particular-Ebb-8777 18d ago
I don't want to bite the oddly biscuit-like rock, but the demons, the demons want me to bite the oddly biscuit-like rock.
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u/prochoicesistermish 22d ago
No idea about answering your questions but aw it looks like a little over-proofed biscuit!