MINERALS AND ROCKS

The science that explores the formation and classification of rocks is called petrology. An important point to note is that rocks make up the lithosphere – a solid mass of rocks with a thickness of 5 to 70 kilometers, which encompasses the Earth’s crust (the solid surface layer of the planet Earth) and the Earth’s upper mantle (the thickest layer containing the majority of our planet’s material). Just beneath the solid lithosphere lies the central part of the Earth’s mantle – the asthenosphere – a layer of partly molten rock called magma. The lower part of the Earth’s mantle maintains a solid state as a result of the high pressure and reaches a depth of up to 2,900 kilometers. Beneath the mantle, all the way to the center lies the Earth’s core, which is made up mostly of iron. By their origin, rocks are classified as igneous, sedimentary and metamorphic. Igneous rocks make up about 95% of the lithosphere, whereas the other two types of rock are only 5% of the lithosphere. Rocks are aggregates of one or more minerals – structures formed by natural physical and chemical processes, with a specific chemical composition and crystal structure, as well as stability under certain temperature and pressure conditions. Minerals can occur as crystals – as a homogeneous, regular geometric solid with some degree of symmetry, which is a reflection of their regular internal composition – the structure. The study of the chemical, structural and physical properties of minerals, as well as the study of the processes of mineral formation and their classification, distribution and their utilization is called mineralogy. Today, there are more than 5,000 known minerals which, based on their chemical composition and structural properties, are grouped into the following classes: Native Elements, Sulphides, Sulfosalts, Oxides and Hydroxides, Halides, Carbonates, Nitrates, Borates, Iodates, Sulfates, Phosphates, Arsenates and Vanadates, Wolframites and Molybdates, Organic Compounds and a large group of Silicates that make up 95% of the Earth’s crust.Biserka Radanović-Gužvica, Croatian Natural History Museum