2014Minerals & Rocks - First Day Cover

Science which examines the origins and classification of rocks is called petrology while the minerals which build rocks are the subject of investigation of mineralogy. Rocks which are known to us build the solid part of the Earth, called lithosphere, which encompasses the crust and the uppermost mantle and reaches until the depth of 100 kilometres. Beneath the lithosphere there is a 2900 kilometres thick layer or mantle, and further to the centre of the Earth, until the depth of 6370 kilometres, there continues the core.
Rocks are aggregates of one or more kinds of minerals, while minerals are natural parts whose composition can be expressed by chemical formula. Minerals are characterised by regular inner structure and regular position of atoms, which is reflected also on the outer form of a mineral (such regular forms of minerals are called crystals).
By its origin rocks can be eruptive sedimentary or metamorphic. About 95% of the lithosphere is composed of magmatic rocks, while the other two types share the remaining 5%. If a rock is composed of just one mineral it is called monomineralic while rocks which contain more minerals are called polymineralic rocks.
Minerals (today there are more than 4700 known are classified according to their chemical composition into elements, sulphides, chalcogenides, oxides and hydroxides, carbonates and nitrates, borates, sulphates, phosphates and a large group of silicates which participate with more than 95% in the building of Earth crust.