A mineral is a naturally present inorganic substance, which is often characterised by an exact crystalline structure. The chemical structure (atomic construction) may be exact, or it may vary. Elements that are naturally present may also be called minerals. A mineral is an economic commodity. Minerals are excavated, because they contain costly matter or specific properties, or because they are pretty or rare. We can distinguish about three thousand different types of minerals. However, new types of minerals are still to be discovered.
All minerals can be divided up in classes. These classified groups have different names, for instance: elements, sulphides, oxides, halides, carbonates, nitrates, borates, sulphates, chromates, phosphates, arsenates, or silicates. A number of these classes have their own subcategories. All minerals belong to different crystalline structure classes, which are divided up after the arrangement of atoms in a mineral. Minerals have distinctive properties, such as colour, hardness, crystalline structure, specific gravity, glow, breakage and solidity. These properties may differ even for minerals of the same type. Many kinds of minerals own specific properties, which clearly distinguish them from other minerals, simply because other minerals do not own these properties. Examples of these specific properties are fluorescence and radioactivity.
Properties of minerals
Mineral fission When you look at crushed kitchen salt with a magnifying glass, you can clearly see that the grains own a pointy, angular or square structure. When salt grains are crushed further, the grains still have the same structure. The only difference is that they are smaller than they where before. This is a specific property of minerals, called mineral fission. When fission takes place, minerals are crushed into smaller grains, while their geometrical structure stays intact. The fission can be either eminent, good, unclear or fully absent. Some minerals, such as opal, cannot be crushed by fission. This basically means that these minerals lose their crystalline structure while they are crushed, or even that they do not own a crystalline structure at all. Such minerals hardly occur.
Elementary cells When we keep on grinding kitchen salt, we will eventually get the smallest salt particles on earth. These are called elementary cells; the smallest possible units of a mineral. Elementary cells possess the same structure as the original salt they derive from.
Crystalline structures The specific appearance of minerals exists, because the atoms that are its building blocks are arranged in the same specific way. Substances that own such a repeating structure are called crystals. Each mineral has its own crystalline structure with its own specific properties, apart from a few exceptions, such as opal. Unfortunately not every crystalline structure is as plain as that of kitchen salt. Some structures are so very complex that they can only be unravelled by means of X-rays.