The rocks are aggregates of various minerals, although, sometimes, they can be formed by a single mineral. Rocks can be formed in many different ways and at different depths. Once formed, they surface. They are found all over the earth's surface.
To study them, we divide the rocks into three large groups, according to how they have formed: igneous, formed by the solidification of magma; metamorphic, formed by transformation of other types and sedimentary, originated from the erosion materials accumulated in a specific area.
Igneous rocks are formed by the cooling and solidification of molten rock matter, magma. Depending on the conditions under which magma cools, the resulting rocks may have coarse or fine granules.
Igneous rocks are subdivided into two large groups:
The rocks plutonic or intrusive they were formed from a slow and deep cooling of magma. The rocks cooled very slowly, thus allowing the growth of large crystals of pure minerals. Examples: granite and sienite.
The rocks volcanic or extrusive, they are formed by rapid and surface cooling, or near it, of magma. they formed by ascending molten magma from the depths filling cracks near the surface, or by magma emerging through volcanoes. Subsequent cooling and solidification were very fast, resulting in the formation of fine-grained minerals or glass-like rocks. Examples: basalt and rhyolite.
There is a mineralogical correspondence between plutonic and volcanic rocks, so that the rhyolite and granite have the same composition, as well as the gabbro and basalt. However, the texture and appearance of plutonic and volcanic rocks are different.
Igneous rocks, composed almost entirely of silicates, can be classified according to their silica content. The main categories are acidic or basic. At the end of the acidic or siliceous rocks are granite and rhyolite, while the basic ones include gabbro and basalt. The diorites and andesites are intermediate
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