Intrusive igneous rocks crystallize below Earth’s surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are: diabase, diorite, gabbro, granite, pegmatite, and peridotite. Dacite is a fine-grained, extrusive igneous rock that is usually light in color.

Something else that fits into Geologic Principles and basic stratigraphy (study of rock layers) are unconformities. Unconformities are simply gaps (missing data) in the rock record, these gaps could indicate a variety of processes. Such as: erosion, deformation, or changes in sea-level.

Extrusive, or volcanic, igneous rock is produced when magma exits and cools above (or very near) the Earth’s surface. These are the rocks that form at erupting volcanoes and oozing fissures.

Mafic rock, in geology, igneous rock that is dominated by the silicates pyroxene, amphibole, olivine, and mica. Mafic rock is commonly contrasted with felsic rock, in which light-coloured minerals predominate. Common mafic rocks include basalt and its coarse-grained intrusive equivalent, gabbro.

Two factors determine what type of rock forms. The composition of the magma determines if the rock is mafic, felsic, or intermediate. The rate the magma cools determines the texture of the rock.

Chemically, mafic rocks are enriched in iron, magnesium and calcium and typically dark in color. In contrast, the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium. The mafic rocks also typically have a higher density than felsic rocks.

Mafic minerals crystallize at higher temperatures, which Bowen’s Reaction Series describes. Therefore, rocks composed of mafic minerals are formed at higher temperatures. They are found in locations deep within the earth and also in tectonic spreading environments, like the seafloor.

Granite is an example of a felsic intrusive rock, while gabbro and diabase are examples of mafic intrusive rocks. Marble is metamorphosed limestone created by contact metamorphism, meaning it is heated through contact by a large igneous intrusion.

Mafic describes magma or igneous rock that is rich in magnesium and iron and is generally dark in color. mineral olivine are responsible for the dark color of mafic rock.

Being that oxygen and silicon are the most abundant elements in magma, geologists define magma types in terms of their silica content, expressed as SiO2. These differences in chemical composition are directly related to differences in gas content, temperature, and viscosity.

Magmas can vary widely in composition, but in general they are made up of only eight elements; in order of importance: oxygen, silicon, aluminum, iron, calcium, sodium, magnesium, and potassium (Figure 3.2.

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the formation of magma are temperature, pressure, water content, and mineral content. gradient. increases the rock’s melting point.