Porphyritic Texture Examples

Porphyritic textures occur in coarse medium and fine grained igneous rocks.

Porphyritic texture examples. Porphyritic texture is a very common texture in igneous rocks in which larger crystals phenocrysts are embedded in a fine grained groundmass. Porphyritic texture is really a subtype but usage of the term often confuses the beginner. K feldspar phenocrysts in this sample. Andesite porphyry and rhyolite porphyry.

Examples of phaneritic igneous rocks are gabbro diorite and granite. Porphyritic structure may appear in any igneous rock but the true porphyries are rocks in which there is a marked. 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. This name refers to the structure which is formed of larger crystals set in a fine grained or glassy ground mass.

Porphyritic textures develop when conditions during cooling of a magma change relatively quickly. Porphyry is an igneous rock characterized by porphyritic texture. The earlier formed minerals will have formed slowly and remain as large crystals whereas. Rocks with porphyritic por fi rit ic texture like this andesite have larger mineral grains or phenocrysts feen o crists in a matrix of smaller grains.

Porphyritic rocks the two images below show a hand sample and a thin section of porphyritic aphanitic textured rocks. Porphyritic texture also occurs when magma crystallizes below a volcano but is erupted before completing crystallization thus forcing the remaining lava to crystallize more rapidly with much smaller crystals. The earlier formed minerals will have formed slowly and remain as large crystals whereas. Porphyry is an igneous rock that contains larger crystals phenocrysts in a fine grained groundmass.

Usually the larger crystals known as phenocrysts formed earlier in the crystallisation sequence of the magma. 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. Imperial porphyry porphyritic metadacite to porphyritic meta andesite by james st. One example of this type of porphyritic texture is a porphyry an igneous rock with large grained crystals interspersed with fine grained usually silicates.

Porphyritic texture porphyritic texture is an igneous rock texture in which large crystals are set in a finer grained or glassy groundmass. The porphyritic structure may be plainly visible the larger crystals being easily seen phenocrysts or it may require the microscope to bring it out. In other words they display two distinctive sizes of grains that are visible to the naked eye. Porphyritic rocks are composed of at least two minerals having a conspicuous large difference in grain size.

John via flickr is licensed under cc by 2 0.