Introduction  (Page 2/3)

A rock is a combination of one or more minerals. Granite for example, is a rock that is made up of minerals such as SiO ${}_2$ , Al ${}_2$ O ${}_3$ , CaO, K ${}_2$ O, Na ${}_2$ O and others. There are three different types of rocks, igneous , sedimentary and metamorphic . Igneous rocks (e.g. granite, basalt) are formed when magma is brought to the earth's surface as lava, and then solidifies. Sedimentary rocks (e.g. sandstone, limestone) form when rock fragments, organic matter or other sediment particles are deposited and then compacted over time until they solidify. Metamorphic rock is formed when any other rock types are subjected to intense heat and pressure over a period of time. Examples include slate and marble.

Many of the elements that are of interest to us (e.g. gold, iron, copper), are unevenly distributed in the lithosphere. In places where these elements are abundant, it is profitable to extract them (e.g. through mining) for economic purposes. If their concentration is very low, then the cost of extraction becomes more than the money that would be made if they were sold. Rocks that contain valuable minerals are called ores . As humans, we are particularly interested in the ores that contain metal elements, and also in those minerals that can be used to produce energy.

Ore

An ore is a volume of rock that contains minerals which make it valuable for mining.

Rocks and minerals

1. Where are most of the earth's minerals concentrated?
2. Explain the difference between a mineral , a rock and an ore .
3. Carry out your own research to find out which elements are found in the following minerals:
   1. gypsum
   2. calcite
   3. topaz
4. Which minerals are found in the following rocks?
   1. basalt
   2. sandstone
   3. marble

A brief history of mineral use

Many of the minerals that are important to humans are metals such as gold, aluminium, copper and iron. Throughout history, metals have played a very important role in making jewelery, tools, weapons and later machinery and other forms of technology. We have become so used to having metals around us that we seldom stop to think what life might have been like before metals were discovered. During the Stone Age for example, stones were used to make tools. Slivers of stone were cut from a rock and then sharpened. In Africa, some of the stone tools that have been found date back to 2.5 million years ago!

It was the discovery of metals that led to some huge advances in agriculture, warfare, transport and even cookery. One of the first metals to be discovered was gold , probably because of its beautiful shiny appearance. Gold was used mostly to make jewelery because it was too soft to make harder tools. Later, copper became an important metal because it could be hammered into shape, and it also lasted a lot longer than the stone that had previously been used in knives, cooking utensils and weapons. Copper can also be melted and then put into a mould to re-shape it. This is known as casting .