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  2. Extrusive rock - Wikipedia

    en.wikipedia.org/wiki/Extrusive_rock

    Shield volcanoes are large, slow forming volcanoes [6] that erupt fluid basaltic magma that cools to form the extrusive rock basalt. Basalt is composed of minerals readily available in the planet's crust, including feldspars and pyroxenes. [2] Fissure volcanoes pour out low viscosity basaltic magma from fissure vents to form the extrusive rock ...

  3. List of rock types - Wikipedia

    en.wikipedia.org/wiki/List_of_rock_types

    The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.

  4. Igneous rock - Wikipedia

    en.wikipedia.org/wiki/Igneous_rock

    Extrusive igneous rock, also known as volcanic rock, is formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, rapidly solidifies. Hence such rocks are fine-grained or even glassy. Basalt is the most common extrusive igneous rock [9] and forms lava flows ...

  5. Glossary of geology - Wikipedia

    en.wikipedia.org/wiki/Glossary_of_geology

    Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Rocks containing amygdules can be described as amygdaloidal. anatexis Melting of pre-existing rock. Compare metatexis, diatexis, and ...

  6. Igneous textures - Wikipedia

    en.wikipedia.org/wiki/Igneous_textures

    When extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals. The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite.

  7. Porphyritic - Wikipedia

    en.wikipedia.org/wiki/Porphyritic

    In extrusive rocks, the phenocrysts are surrounded by a fine-grained (aphanitic) matrix or groundmass of volcanic glass or non-visible crystals, commonly seen in porphyritic basalt. Porphyritic intrusive rocks have a matrix with individual crystals easily distinguished with the eye, but one group of crystals appearing clearly much bigger than ...

  8. Rock cycle - Wikipedia

    en.wikipedia.org/wiki/Rock_cycle

    The rock cycle is a basic concept in geology that ... may cool very rapidly on the Earth's surface exposed to the atmosphere and are called extrusive or volcanic rocks.

  9. QAPF diagram - Wikipedia

    en.wikipedia.org/wiki/QAPF_diagram

    QAPF diagram for classification of plutonic rocks. A QAPF diagram is a doubled-triangle plot diagram used to classify intrusive igneous rocks based on their mineralogy.The acronym QAPF stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)", which are the four mineral groups used for classification in a QAPF diagram.