Anatomia di un poeta

Rocks

Rocks

Rock is an aggregate of minerals and/or mineraloids. The Earth's  outer solid layer  (lithosphere ) is made of rock. There are  three types  of rocks;

igneous, sedimentary, and metamorphic.

Petrology is the  scientific study of rocks. Rocks are classified:

-by Mineral and chemical composition;

-by the texture of the constituent particles;

-by the pressure that formed them.

These indicators separate rocks into ignenous, sedimentary and metamorphic.

ignenous  rocks are formed when molten magma cools. They are divided into two main categories.

- plutonic or intrusuve rocks magma cools and crystallizes slowly within the earth's crust.

-volcanic or extrusive rocks magma reaches the surface either as lava or fragments ejecta (pumice and bassalt).

Sedimentary rocks arte formed by depositionm of clastic sediments, organic matter, chemical precipitates (evaporities)

Pariculate  and cementation compact  during diagenesis matter and  cementation compact during diagenesis. Sedimentary rocks form at  or near the Earth's surface. Mud rocks comprimes 65% (mudstones, shale, and  silstone); sandstones 20 to 25% and carbonate rocks 10 to 15% (limestone and dolostone). Metamorphic  rocks are formed by subjescting any rock type to high temperatures and pressure.These temperatures and pressure  are always higher than those at the Earth's surface. They change the original minerals into other mineral type or else into other forms of the same minerals ( for example by recrystallisation).

The three classes of rocks -the igneous, the sedimentary and the metamorphic- are subdivided into many groups. Therer are however, no boundaries between allied rocks. By increase or diminution in the proportions of their constuent minerals, they pass  by every gradation into one another. Therefore the definition corespiond to selected points in a graduated series. Rocks have had a grat importance in the technological advancement of the human race.. Rocks  have been used by Homo sapiens and other hominids for more than 2 million years.

The mining of rocks has been one of the most important factors  of human advancement. It has pregressed at different ratesin different  places because of the kind of metals found in that region. The prehistory and history of civilazition is classified into the Stone Age, the Bronze Age and the Iron Age. Rock is still used to construct buidings and infrastructure. When used for these puroposes, rocks are called dimension stone.