Chalk, limestone, and dolomite are all basically made from calcium carbonate. This comes from a mixture of minerals and pieces of animals (especially animal shells). They are mostly formed in oceans. Shales, sandstones, and conglomerates are all clastic rocks. They are made from pieces of other rocks. The pieces may have come from erosion by water, ice or wind. Coal is made from ancient plants; oil and natural gas is also organic in origin.
Some sedimentary rocks are made of just one type of sediment, all about the same size, such as sand. Other sedimentary rocks will have large and small lumps, and pieces of different types of rock. Well-known sedimentary rocks are sandstone and limestone.
Sedimentary rocks may be found anywhere on Earth. When sedimentary rocks are heated and squeezed, they become metamorphic rocks. Igneous rocks have a volcanic origin. Over a very long time, rocks get recycled, in two ways. When marine sediments are raised above sea level, they get weathered, and the pieces carried down to the sea. On a much longer time-scale continental plates may collide. Then one plate goes under the other (is subducted), and all its material is recycled, emerging much later.

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