A mineral is a chemical compound or element having a crystal structure, which as a solid in a state of nature occurs and is formed by geological processes. The science that studies called mineralogy minerals, this area of science has often overlap with chemistry because mineralogy also studies the composition of minerals. Minerals are in the field, often identified by their crystal form, their color, their stripe color (the color that they give off when they are scratched), their hardness, their melting behavior, their association with other minerals, etc. The classical form of recognition requires a lot of experience and is not always reliable. Geology is one reason more and more to rely on retrospective analysis of different optical properties than color, especially by polarizing microscopy (light microscopy with polarized light), X-ray powder diffraction, X-ray fluorescence spectrometry, electron beam micro analysis (electron microprobe) and atomic absorption spectrometry . In some cases, infra-red analysis is applied. Minerals in Europe are generally divided into nine groups according to the classification of Strunz. In the United States, the format used primarily according to Dana, wherein minerals are divided into 78 groups. Each group of the classification of Strunz comprises elements or compounds having a specific structure. Africa is in area the second largest continent on Earth. Only Asia is larger. If, however, North and South America as one continent, Africa is in third place. It covers approximately 30.24405 million square kilometers (mainland and islands together), which is 20.3% of the total land surface of the earth. There are more than 1 billion people, which is about one-seventh of the world. Virtually the whole of Africa belong to the Third World. Some people count the continent to this point, others only the countries south of the Sahara, excluding South Africa.