Both extrusive and intrusive igneous rocks are derived from magmas. The temperature and pressure conditions in the crust and upper mantle influence the melting temperatures of the minerals in the rocks .
Temperature and pressure increase with depth from the surface and eventually reach a point at which rocks melt . The geothermal gradient is the rate at which temperature increases with depth. In the upper crust, the geothermal gradient is about 2 .5 degrees centigrade for every 100 meters (330 feet).
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Intrusive rocks crystallize from magmas that have been intruded into the earth’s crust at depths far below the surface. These intrusions are then usually exposed millions or billions of years later through the processes of uplift, mountain-building, and erosion . Other intrusive rocks are discovered through deep-drilling programs. Country rock is the surrounding rock that the magma invades . A contact then separates the cooled intrusive rock from the country rock.
Contacts are rarely straight lines, are quite irregular, and mark the change in rock type. The edge of the intrusive rock is usually very fine grained because it is here where the most rapid cooling took place. This edge of the intrusion is called the chill zone.
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Earth with its beauty also got nature destruction from the inside. The core of the earth that form volcanoes and start blowing lavas. Those two things we will discuss it more further in below articles.
Volcanism, or volcanic activity, is the venting of liquid magma at the surface of the earth. Occasionally explosive, the process is important in producing continental and oceanic crust . Volcanoes are hills or mountains that form around the vent and consist of cooled magma, rock fragments, and dust from the eruptions .
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