Sedimentary rocks are formed from layers of deposits laid down in
lakes or seas. Over millions of years the layers of sediment build up
resulting in the weight pressing downwards, creating high pressure,
which squeezes the water out. As the water is squeezed out, salts form
between the particles of sediment due to crystallization and this
cements the particles together. Sedimentary rocks can either rise to
the surface again to be discovered, or they can descend into the heat
and pressure below.
Sandstone is a type of sedimentary rock and is formed from sand.
Sandstone is fine particles of sand cemented firmly together due to
heat and pressure, which is why it looks very much like sand. However,
there is red sandstone as well as yellow. Sandstone is commonly used
Limestone, which can also be called chalk, is formed from seashells.
It mostly contains calcium carbonate as seashells are made from
calcium carbonate. It is usually white or grey in colour. The original
shells are mainly crushed down how some fossilised shells can still be
found in limestone.
Mudstone, which is also known as shale, is formed from mud. Mud is
basically finer particles of sand cemented together due to heat and
pressure. Mudstone is often grey in colour and unlike other rocks; it
tends to split onto its original layers very easily.
Coal is a fossil fuel formed from the remains of plants and
vegetation. Most of our coal was formed about 300 million years ago
when the earth was covered by steamy swamps. As plants and trees died,
their remains sank to the bottom of the swampy areas building up in
layers. Due to the heat and pressure, the particles are compressed
together is coal is formed.
The chemical composition of limestone is CaCO3, which makes it a
compound of calcium and carbon dioxide, (calcium carbonate).
As limestone is mainly calcium carbonate CaCO3, a simple test to see
whether a given rock is limestone would be to add hydrochloric acid to
it. It the substances is limestone, carbon dioxide should be given
off. When hydrochloric acid is added to limestone, it the solution
should fizz giving off a colourless gas that turns limewater milky,
which is carbon dioxide CO2.
Calcium carbonate + Hydrochloric acid = Calcium chloride + water +
CaCO3 + 2HCl = CaCl2 + H2O + Co2
When limestone is heated at a high temperature, carbon dioxide and
calcium oxide, which is also known as quicklime is produced.
[IMAGE]Calcium carbonate calcium oxide + carbon dioxide
[IMAGE]CaCO3 CaO + CO2
Calcium oxide, or quicklime reacts violently with water to produce
calcium hydroxide, which is also known as slaked lime. Slaked lime is
a white powder and a very strong alkali, and because it is an alkali
it can be...