Petrographical properties: structure, chemistry, mineral

There is an impressive diversity of natural stone. In Central Europe more than 500 varieties, worldwide about 5000, are offered by the trade. And as every type of stone exhibits specific properties and features, the potential applications are correspondingly diverse. Petrography is the study of rocks. The usability of a stone is determined by its petrographical, i.e. mineralogical and chemical, features, plus a number of technical parameters.
Petrographical properties: structure, chemistry, mineral
content (color, crystallinestructure and hardnes)..
Technical parameters; density (true density, bulk density and
porosity), strength (compressive, flexural and abrasion resistance), thermal conductivity, thermal expansion, heat resistance, freeze-thaw behavior, water absorption and resistance to chemicals.
Good thermal conductivity is important when stone is used as a floor covering. Stone floors are often perceived as cold because they conduct heat away from the body. However, their heat storage capacity can be a great advantage, also in conjunction with underfloor heating.
Properties
Plutonic rocksNamed after the god of the underworld, these rocks are formed by the full crystallization of "mobilised magma" in the Earth's crust. The usually - uniform, non-directional and dense structure is due to the gradual cooling. The varying mineral composition gives rise to rock types like granite, diorite and gabbro. Almost all plutonic rocks are frost-resistant and are popular in building owing to their high compressive strength and hardwearing qualities. Some igneous rocks, e.g. granite, can exhibit above-average natural radioactivity in some circumstances.
Hypabyssal rocks These types of rock are formed when small amounts of magma solidify within the Earth‘s crust in volcanic vents or fissures. Their structure is similar to the plutonic rocks but the faster cooling process results in non-uniform crystallization with phenocrysts of other material. This subdivision includes pegmatites, aplites and lamprophyres.