Sedimentary rocks form from
of the Earth's crust is made of igneous
rock, on the very surface
sedimentaries cover about 80% of the Earth's surface.
They are formed near the Earth's surface, where sediments accumulate on
the sea/ocean bottom, in riverbeds, in deserts and on beaches.
layers push the older ones down, which lithify under the
pressures from the layers above.
are formed from rock matter eroded by physical weathering.
are formed from rock material eroded by chemical weathering.
are formed from parts of dead plants and animals.
Another way of grouping them is by grain
Because the sediments are transported before they are deposited, they
are sorted by grain size. That is why the new rocks tend to have quite
uniform grain size.
Mark via Flickr.com
Sedimentaries are very valuable for scientists when working out
The presence of fossils
in some sedimentaries is a big help there, not only with
ages, but also because it makes it possible to work out in what
conditions a rock formed.
Sedimentaries are the only type of rocks that
rocks never do, and metamorphics can do very rarely.