A mineral is a homogeneous inorganic natural substance of a definite chemical composition, it is usally a solid, but occasionally a liquid. A few are composed of a single element, but most are formed by the combination of several elements. A product which has developed by a natural process is a natural substance. A mineral is homogeneous physically and chemically when it consists of elements of the same kind throughout. In this a mineral differs from rock, which is also an inorganic natural substance, but one composed of different minerals, and which, in contrast to them, forms large parts of the earth’s crust. There are some rocks (for instance sandstone or limestone), which consist almost entirely of one mineral (quartz or calcite for example). We do not classify them as minerals, for they do not have to be homogeneous, as do minerals. The science which studies minerals is called mineralogy. It not only observes and defines the various characteristics of minerals, but also explains their origin and development. Petrography concentrates on studying rocks. These sciences, together with geology, which studies the origin, composition and evolution of the earth, are not just theoretical sciences. Their findings affect practical life with ever increasing force. The vast and vital role that minerals and rocks play in the modern world is taken for granted. They form the basic raw materials of industry, whether they are metallic minerals extracted from ores, minerals for the chemical, glass or ceramic industry, or others.
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