A mineral is a naturally occurring substance of a single kind. It is different from a rock, which may be made of many minerals. There are nearly five thousand known minerals. Nine out of ten of these are related to sand, that is they are made mostly of the element silicon and oxygen. Geologists call these minerals silicates. The reason for this is that three quarters of the crust of the earth is made of silicon and oxygen.

Every mineral is made of a unique combination of elements and it has its own properties. Minerals may also grow into crystals with flat faces. When this happens, it becomes very much easier to tell what they are. For example, the mineral iron pyrites gas square box (cubic) crystals made of a good-looking colour. It is actually commonly known as fool's gold. The mineral calcite, which is made of carbon , calcium and oxygen, is like a box that has been usher to one side. It has white to transparent crystals. Crystals of minerals that people choose to value are called gemstones. Ruby is a gemstone made of aluminium, silicon and oxygen.

Beside the silicates (which includes minerals like amethyst), the main groups are native elements (like gold and copper), sulphides (like iron sulphide mentioned above), oxides (like Bauxite (aluminium oxide) from which we get aluminium), halides (sodium minerals from which we get salt), carbonates (calcium minerals including calcite), sulphates (like gypsum), and phosphates (like turquoise).