Home Igneous Rocks Metamorphic Rocks
Most
of these are made from Sediment (Wow!) – bits of rock fragments, which have
sunk to the bottom of rivers, or more usually the sea. They then get buried
& squashed. Over time the fragments get stuck together to form rock. This
happens because water also gets trapped with the sediment. Chemicals dissolved
in the water make a form of ‘glue’.
Chalk & Limestone, however, are made from the shells of dead sea animals.
Made
from gravel, cemented together.
Made
from sand, cemented together.
Made from mud, cemented together.
Both of these are rich in Calcium carbonate [ Ca CO3]. This comes from the animal shells that these rocks contain. It is an alkali, and so these rocks effervesce - or fizz with dilute acid.
Chalk;
Chalk is made from almost pure animal shells, and so tends to be white in colour.
Limestone;
Limestone is a mixture of both animal shells and mud. This gives it its grey colour.
