Rocks and Minerals

The inner parts of the Earth consist of rock which is melted and fluid, and which is called magma. On top of the magma, there is a thin and hard layer of rock, the earth’s crust. The crust consists of several types of rock, which can be sorted into groups according to how they’ve been created. [1.] Some of the rock used to be magma from within the earth. This magma reached the surface as lava during a volcanic eruption, and then solidified into stone. This is igneous rock.

Igneous rock is often black, for instance in the cases of diabase or basalt. But there are other types of igneous rock which solidified without having been pushed to the surface of the earth. One example is granite, which is often lighter in colour, with darker dots. [2.] Rivers bring particles of sand and clay to the ocean. The particles sink to the ocean floor and form sediment. Over the course of millions of years the sediment forms thick layers which are compressed so hard that they are transformed into rock.

This is sedimentary rock. In the rock, the different layers of sediment are clearly visible. Examples of sedimentary rocks are sandstone and limestone. Limestone is formed when shells from small organisms sink to the ocean bed and are compressed into stone. Sedimentary rocks cover almost all the surface of the earth, and all of the ocean bedrock.

All fossils from dead organisms are found in sedimentary rocks. Therefore, by studying sedimentary rocks we can better understand the evolution of life and previous conditions on earth. In sedimentary rocks there are also important natural resources. Energy sources like oil and gas are extracted from the sedimentary bedrock. [3.] If the rock is compressed even more, and is also pressed deeper into the bedrock, both pressure and temperature rise. The rock then melts and changes.

When it solidifies into rock again, new kinds of rock are formed. Sandstone is transformed into gneiss. Limestone is transformed into marble. These are examples of metamorphic rocks. A piece of rock consists of one or several substances.

These substances are called minerals. Examples of minerals are diamond, quartz and feldspar. Many minerals contain some sort of metal. If a mineral contains so much metal that it is worth extracting this from the mineral, the mineral is called ore. One example is iron ore, which exists in different forms, like the minerals magnetite and hematite.

These are extracted by mining, and then the ore is enriched in order to obtain pure iron. Other types of ore that have become increasingly important in recent years are those that contain lithium, since lithium is very commonly used in batteries. The rocks of the earth are grouped according to how they are formed. Igneous rocks are created from magma from the centre of the earth. Sedimentary rocks are formed from sand, clay, and organic material which are compressed together.

Rock which has been transformed is called metamorphic rock. Rock consists of one or several minerals. A mineral which is extracted by mining in order to obtain metal is called an ore.