Kinjal Juthani

11 Q        Science Assessment

Sedimentary Rocks

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 for buildings.

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.

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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 ...

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