Porphyritic Texture Igneous Rock

K feldspar phenocrysts in this sample.

Porphyritic texture igneous rock. Porphyritic texture is really a subtype but usage of the term often confuses the beginner. Igneous textures include the rock textures occurring in igneous rocks igneous textures are used by geologists in determining the mode of origin igneous rocks and are used in rock classification. Phaneritic aphanitic porphyritic glassy pyroclastic and pegmatitic. There are nine main types of igneous rock textures.

Porphyritic structure may appear in any igneous rock but the true porphyries are rocks in which there is a marked. What determines igneous rock texture. This name refers to the structure which is formed of larger crystals set in a fine grained or glassy ground mass. Porphyritic rocks are composed of at least two minerals having a conspicuous large difference in grain size.

Each kind of texture has a variety of different characteristics that make them unique. Porphyritic rocks the two images below show a hand sample and a thin section of porphyritic aphanitic textured rocks. The specimen shown is about two inches five centimeters across and has a porphyritic texture. The porphyritic structure may be plainly visible the larger crystals being easily seen phenocrysts or it may require the microscope to bring it out.

Porphyry is an igneous rock that contains larger crystals phenocrysts in a fine grained groundmass. Many rocks with an overall fine grained texture display scattered minerals that are more than 1 mm across. There are six main types of textures. Phaneritic vesicular aphanitic porphyritic poikilitic glassy pyroclastic equigranular and spinifex.

Porphyritic rocks may be aphanites or extrusive rock with large crystals or phenocrysts floating in a fine grained groundmass of non visible crystals as in a porphyritic. Porphyritic is an adjective used in geology specifically for igneous rocks for a rock that has a distinct difference in the size of the crystals with at least one group of crystals obviously larger than another group. Phaneritic aphanitic porphyritic glassy pyroclastic and pegmatitic. This chart shows that andesite is typically composed of plagioclase amphiboles and micas.

Usually the larger crystals known as phenocrysts formed earlier in the crystallisation sequence of the magma. Porphyritic texture porphyritic texture is an igneous rock texture in which large crystals are set in a finer grained or glassy groundmass. There are six main types of textures. Aphanitic a not phaner visible rocks in contrast to phaneritic rocks typically form.

Sometimes with minor amounts of pyroxenes quartz or orthoclase. Igneous textures include the rock textures occurring in igneous rocks igneous textures are used by geologists in determining the mode of origin igneous rocks and are used in rock classification. Porphyry is an igneous rock characterized by porphyritic texture. The large crystals are termed phenocrysts while the aphanitic rest of rock is.

This porphyritic texture indicates that the magma sat and cooled a bit below the earth s surface thus giving time for the large crystals to grow before erupting onto the surface and cooling very quickly. Porphyritic texture is a very common texture in igneous rocks in which larger crystals phenocrysts are embedded in a fine grained groundmass.