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Apologies in advance for a beginners question. Different rock types make me curious and recently went to an area where interesting sedimentary rock is all over. As the area is on the coast, sea has washed away some soil and is making it easy to observe rocks.

This sedimentary rocks is composed of different pieces. Sometimes the pieces are in different color, while other times are white. I took an image of a typical rock:

sedimentary rock - first view sedimentary rock - second view

How such sedimentary rock is made? In which period of crust formation? Can you point me to links where I can learn more about it?

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The rock you show is a conglomerate - it contains a substantial amount of clasts (your pieces) that are gravel or larger size. The pieces have been cemented together into a new rock - kind of like concrete.

There are a couple of additional things that can be seen in your pictures. First the clasts are very angular. This means they haven't been rounded be wave action or transport to the location where the rock formed. It was very likely formed close to where you found it. If you look at the clasts, the grey ones look like the rock to the lower left and the light ones seem similar to the rock to the lower right. This suggests that the conglomerate formed by eroding those rock types followed by cementation very close to the source. Then a new phase of erosion formed the pieces you see.

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I would not say there is any one answer of how sedimentary rocks are formed, they are a wide class of rocks, and certainly they were not formed in one period, in fact they are still regularly forming.

The class includes sand stones, mud stones, lime stones, concretions as you show, and many other forms. Basically they are sediments (thus the name) that pile up and fuse or bond through chemical reactions, pressure or other reaction and form larger composites.

A fair starting point is Wikipedia: https://en.wikipedia.org/wiki/Sedimentary_rock

On your particular pictures, that would be fairly typical or a glacial gravel deposit, riverbed deposits or even a landslide which was then filled in with silt and other deposits which fused into a cement or limestone encasing the gravel.

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