For thousands of years the humans have been using rocks as tools. In addition, they are used for constructing roads, buildings, as well as for creating a great variety of art.
Minerals are natural substances having a certain chemical composition and physical properties. These consist either of only one chemical element, such as, for example, gold or silver, in general, however, they are compounds. That is to say, they are solid compositions occurring in the earth’s crust, earth’s mantle, and in some heavenly bodies such as moons or meteorites.
Rocks are mineral deposits. However, only 250 of a total of 2000 different kinds of minerals form rocks. The most important ones belong to the group of silicates. In accordance with their origin, the rocks are classified into igneous, sedimentary, and metamorphic. Loose rocks, such as gravel and sand, are also included here.
Almost all rocks we see come from the earth’s crust. Three quarters of the crust are made up of oxygen and silicone. It also includes organic residues, such as coal, as well as liquids, such as water, oil, or gases. Aluminium, iron, calcium, sodium, potassium, magnesium, and other minerals are important elements. Although it seems that rocks are rigid and constant, they do undergo many changes. The earth’s surface is continually renewed by the rock cycle.
Igneous, or volcanic, rocks are expelled from the earth’s interior to the surface, they erode and become sedimentary. Sedimentary rocks change into metamorphic, they melt, and again turn into igneous. On the earth’s surface, sedimentary rocks are the most common. Metamorphic and igneous rocks are predominant underneath the earth’s crust.
