[Just thinking (OP)]

Have you ever wondered how pebbles form. If you look in most rivers you will see many millions of pebbles the strange thing is that they are for the most part the same size certainly at least fit in your hand size. Yes, there are the big ones but not that many to suggest that the process of pebble formation is due to the pebbles wearing down from tumbling and water wear as there are no moor pebbles to replenish this process. A friend told me once that all the little pebbles started out as huge boulders and I laughed and replied that is a lot of big boulders. I know if we dig in the ground we can find pebbles all over the earth but this does not address the formation particularly the size range. So it remains a mystery to me. I have a couple of possibilities in mind but I would like to get more ideas.

[Europa]

Have you ever wondered how pebbles form. If you look in most rivers you will see many millions of pebbles the strange thing is that they are for the most part the same size certainly at least fit in your hand size. Yes, there are the big ones but not that many to suggest that the process of pebble formation is due to the pebbles wearing down from tumbling and water wear as there are no moor pebbles to replenish this process. A friend told me once that all the little pebbles started out as huge boulders and I laughed and replied that is a lot of big boulders. I know if we dig in the ground we can find pebbles all over the earth but this does not address the formation particularly the size range. So it remains a mystery to me. I have a couple of possibilities in mind but I would like to get more ideas.

Pebbles are made in a cereal factory

[Colin2B]

Pebbles are made in a cereal factory

If you don’t have a sensible input, don’t make one.

[Colin2B]

I know if we dig in the ground we can find pebbles all over the earth but this does not address the formation particularly the size range. So it remains a mystery to me.

Pebbles are not found all over the earth, but in areas that are or were ocean beaches or rivers, hence the idea that they were formed by the action of water.
In order to form a smooth pebble the rock has to be moved, rolled, etc so it is abraded. This puts a limit on size.

[Bored chemist]

Pebbles are the same size because, if they are a different size, they are not pebbles.
https://en.wikipedia.org/wiki/Grain_size#/media/File:Wentworth_scale.png

[Origin]

How did pebbles form?  The simple concise answer is erosion.

[Just thinking (OP)]

Pebbles are not found all over the earth, but in areas that are or were ocean beaches or rivers, hence the idea that they were formed by the action of water.
In order to form a smooth pebble the rock has to be moved, rolled, etc so it is abraded. This puts a limit on size.

Thanks for your answer and the reason for the uniformity in the size makes good sense I guess they reach a mass that becomes too light to chip away any further.

[Bored chemist]

I guess they reach a mass that becomes too light to chip away any further.

Where do you think sand comes from?

The big reason why, when you see a heap of bits of rock on the beach they are more or less the same size, is that they have just been sorted by the tide and current. It's a bit like panning for gold.

[Just thinking (OP)]

Where do you think sand comes from?

The big reason why, when you see a heap of bits of rock on the beach they are more or less the same size, is that they have just been sorted by the tide and current. It's a bit like panning for gold.

I'm glad you have mentioned sand I guess sand is like miniature pebbles and the sorting by weight and tidal movement is the most likely answer to this having said this is sand more brittle and prone to break down in such small fragments or is sand older and had more time to reach its size.

[Colin2B]

is sand more brittle and prone to break down in such small fragments or is sand older and had more time to reach its size.

The longer you keep grinding something the finer the particles.

The big reason why, when you see a heap of bits of rock on the beach they are more or less the same size, is that they have just been sorted by the tide and current. It's a bit like panning for gold.

I assume you’ve been to Chesil beach and seen them sorted by size from one end to the other

[Just thinking (OP)]

I assume you’ve been to Chesil beach and seen them sorted by size from one end to the other

It still remains a mystery to me as to where such a large amount of rock pieces would have come from. many pebbles that we can see are great distances from any mountains and ranges that could supply such a source.

[Colin2B]

I assume you’ve been to Chesil beach and seen them sorted by size from one end to the other

It still remains a mystery to me as to where such a large amount of rock pieces would have come from. many pebbles that we can see are great distances from any mountains and ranges that could supply such a source.

Chesil beach is not far from rocky cliffs. Many of those cliffs used to be mountain height.

[Just thinking (OP)]

Chesil beach is not far from rocky cliffs. Many of those cliffs used to be mountain height.

Are the pebbles the same compassion as the cliffs? I have seen many pebbles that look a lot like sediment layers mostly clay and think that they may have started out as individual fragments that were at one time dried sunbaked earth like the floor of a desert.

[Origin]

It still remains a mystery to me as to where such a large amount of rock pieces would have come from

I have no idea how this could be such a mystery to you, especially since it has been adequately explained in this very thread.

[Just thinking (OP)]

I have no idea how this could be such a mystery to you, especially since it has been adequately explained in this very thread.

I find it difficult to comprehend that they could be of great age and still be around and yet I can't come up with a more recent reason for them being here. We can find pebbles high in the mountains the mountains erode yet the pebbles do not.

[Bored chemist]

I find it difficult to comprehend that they could be of great age and still be around

They are rocks.
They don't die young.

[Colin2B]

We can find pebbles high in the mountains the mountains erode yet the pebbles do not.

Soft stuff erodes lots, hard stuff less so.

[Colin2B]

Are the pebbles the same compassion as the cliffs?

Cliffs don’t have much compassion. If you fall off or a rock drops on you they just don’t seem to care

I have seen many pebbles that look a lot like sediment layers mostly clay and think that they may have started out as individual fragments that were at one time dried sunbaked earth like the floor of a desert.

Sandstone or claystones are relatively soft, most of the pebbles you see are harder material eg from extreme pressure or volcanic action like granite, slate, marble.

[Just thinking (OP)]

Soft stuff erodes lots, hard stuff less so.

Like a cup of coffee the sugar dissolves but the spoon is still around.