We have evaporites, these are when minerals are produced
by the evaporation of a warm salty sea leaving the minerals behind.
We have sedimentary rocks that are formed by biological or biochemical processes.
>> For instance, we might talk about the carbonates like the calcium carbonate,
the limestones, these are produced by animals that have shells,
they die, their calcium carbonate shells sink to the bottom and
solidify into layers >> There are also
biological sedimentary rocks that are comprised of silica.
These would be something like cherts, and
these would be microfossils that produce silica shells.
Then the fourth one is pyroclastic flows.
These are flows that are erupted by volcanoes, travel and
are laid down in beds.
Now you can see I've underlined it in blue here,
indicating that it's kind of a hybrid between igneous rock being an extrusive,
erupted from the volcano, but it's also laid down in beds.
So there may be instances where we may see ash deposits that are laid down
as sedimentary layers embedded within mudstones or sandstones.
These ash flows can be critical for dating
the layer of rock because of the isotopes within those minerals.