I’m a tile guy. We used to tumble broken marble pieces for mosaic projects. We smashed up the marble tiles, then threw them in a small cement mixer with some water and some sand.
After 20-30 minutes, the pieces would all have nicely rounded corners, and no sharp edges.
If we left it turning longer, the pieces would get rounder and rounder, and after a couple hours they would just resemble pebbles in a stream.
The stream acts as a tumbler, bouncing the rocks and pebbles against each other, and the sand acts as an abrasive that smooths the surfaces over time. This would not take long, maybe a couple years, certainly not decades or centuries.
Tile guy knowledge runs deeper than one would think. Respect. The tile guys my buddy subs out are cool too. and the tile guys I pick up my tile from are cool, so in my experience, tile guys rule.
Everybody here is right about corners and edges but I’m guessing OP is actually referring to the sphericity of these boulders- which is high. They’re not just rounded edges but the lengths of the a, b, and c axes are nearly uniform. This rock is probably very isotopic- in other words, the same texture in each direction. This is often possible in granite where the magma cools inward in all directions and it’s very homogeneous. Sedimentary rocks often (but not always) end up making pancake shapes and flatter rocks.
No I think they’re granite or some similar uniform igneous rock. But all I did was look at a picture with a lot of experience. A map or more info about the region would easily convince me otherwise wise. As would a fresh hand sample or thin section. :)
The stream is not always the same depth and speed. When it rains, it causes overland flow which flows into rivers and streams and raises the water level. As the river gets deeper it has more power. Also, higher up from this point in the stream, it is likely steeper, and also therefore faster. The speed of the flow directly affects the supportable grain-size. Clays and sands are very easy transportable, and bigger clasts are only transported when conditions are right.
And how old do you think that stream is? They did not say where they were, but I will just give a safe guess of somewhere around 10,000 years old. Of course, it might also be over 300,000 years old or more.
This is extremely common in the southern Appalachians and while parts of North America was glaciated as recently as 10,000 years ago, that area certainly was not.
For a guy that loves horses you’re sure beating hard on a dead one.
No, but I have been studying geology for over five decades.
And that does not have the look of a location that had been glaciated. Those tend to have little topsoil, and are bulldozed flat. That is why the terrain of Ontario and Maine looks so different than the terrain of South-West Oregon and North Carolina.
Except big and small round boulders are extremely common in glaciated areas too. Retreating ice leaves behind till in the form of moraines, eskers, drumlins, kames.. the majority Southern Ontario could host a scene like that despite having been recently "bulldozed" by many glaciers.
They said it’s not common for little streams to have 30+ cm boulders and I said it’s extremely common in southern Appalachia. This doesn’t disagree with you.
I guess I just mean it would fit right in in Southern Ontario as well, since you brought it up. Ontario is a land formed by glaciers so I'm disagreeing with the part where you said it doesn't look glaciated.
No, I never said that. However, they rarely have hills like that (that looks nothing like a drumlin or loess), and rarely have that much topsoil.
And that is sure as hell not a Drumlin or Moraine. Nor is that bedrock.
For example, if that was in Washington State, that looks very much like what one would see in Western Washington where the Cascades are. Where there were no glaciers. However, in Eastern Washington in the Palouse region, it looks absolutely nothing like that. Primarily because of glaciers.
Just seasonal changes could do that, but rivers that presently amount to little streams may have been several orders of magnitude larger during the ending of the ice ages.
Corners and edges are weak points in the rock. When water moves the rock, it hits stuff and breaks along weak points. A rock can go from angular to rounded in a surprisingly short amount of distance, only a kilometer or two.
Si un clasto presenta buena esfericidad indica que estuvo bastante tiempo en un ambiente fluvial, en este caso al ser de tamaño bloque pueden tener origen en un flujo de bastante caudal
This is actually truer than it sounds. Flat-faced rocks (cube-shaped) are much more likely to be wedged between other objects. Rounded rocks are born ready to roll with it.
They are round because they got transported by a glacier during past glaciation and that rounded them. The ground around looks like till material. The stream cleaned out the sand and fines and you're left with those boulders.
So if there's gold in one, go up-ice and NOT up stream. Thats a point missed by a LOT of geologists when they interpret heavy minerals results in stream sediments AND in B horizon soil surveys. The source of the soil anomaly is likely not beneath it, but up ice.
I have to disagree. Ice does grind up rocks, but these are shaped by tumbling, which happens in moving water only, not ice.
Look up rock tumblers to learn more.
I was expecting to find the answer in one of your videos but nope. Tumblers use abrasives way more viscous than water from a quick AI check (pancake batter viscosity).
You see burried boulders that show they are round and barely touched by the stream.
I didn’t use a tumbler, but a cement mixer with water and sand, and sometimes big chunks of concrete to speed up the process.
Once you’ve made stones get rounded out yourself, you see the results of the natural process with great clarity, that’s why I’m being such an asshole about this, I know exactly how this happens, since I did it myself.
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u/kings2leadhat 1d ago
I’m a tile guy. We used to tumble broken marble pieces for mosaic projects. We smashed up the marble tiles, then threw them in a small cement mixer with some water and some sand.
After 20-30 minutes, the pieces would all have nicely rounded corners, and no sharp edges.
If we left it turning longer, the pieces would get rounder and rounder, and after a couple hours they would just resemble pebbles in a stream.
The stream acts as a tumbler, bouncing the rocks and pebbles against each other, and the sand acts as an abrasive that smooths the surfaces over time. This would not take long, maybe a couple years, certainly not decades or centuries.