What is a porphyritic texture?
A porphyritic texture displays minerals in two distinct size populations: one or more minerals are consistently larger than the rest of the minerals in a rock. The rest of the smaller mineral grains are called the groundmass. Porphyritic textures are found in rocks with both coarse- and fine-grained groundmasses.
What is Aphanitic texture?
Aphanitic – This texture describes very fine grained rock where individual crystals can be seen only with the aid of a microscope, i.e. the rock is mostly groundmass. An aphanitic texture is developed when magma is erupted at the Earth’s surface and cools too quickly for large crystals to grow.
What is porphyritic texture and how is it interpreted?
Porphyry is an igneous rock characterized by porphyritic texture. Porphyritic texture is a very common texture in igneous rocks in which larger crystals (phenocrysts) are embedded in a fine-grained groundmass. Porphyry is an igneous rock that contains larger crystals (phenocrysts) in a fine-grained groundmass.
What is an aphanitic igneous rock?
aphanitic; from Ancient Greek αφανης (aphanḗs) ‘invisible’) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye).
What does the term porphyritic mean?
Definition of porphyritic 1 : of or relating to porphyry. 2 : having distinct crystals (as of feldspar) in a relatively fine-grained base.
Is porphyritic fine or coarse?
Porphyritic texture is an igneous rock texture in which large crystals are set in a finer-grained or glassy groundmass. Porphyritic textures occur in coarse, medium and fine-grained igneous rocks. Usually the larger crystals, known as phenocrysts, formed earlier in the crystallisation sequence of the magma.
What is a porphyritic granite?
Granites are coarsely crystalline igneous rocks, having a phaneritic texture. Porphyritic granites have a mix of large & small crystals, but all crystals are still fairly decent-sized. Large crystals in a porphyritic rock are called phenocrysts. Porphyritic granites typically have K-feldspar phenocrysts (pinkish).
What does the term aphanitic mean?
Aphanitic is a descriptive term for small crystals, and phaneritic for larger ones. aid of a microscope (called aphanitic, from the Greek aphanēs, meaning “invisible”) or contains no minerals at all (in the latter case, the rock is composed of glass, which is a highly viscous liquid).
What does a porphyritic texture indicate about an igneous rock?
What does a porphyritic texture indicate about the cooling history of an igneous rock? It indicates that crystals were formed at depth (slow cooling) and then the magma moved to a shallow depth or erupted (fast cooling).
What is the difference between porphyritic and pegmatitic textures?
Pegmatitic texture occurs during magma cooling when some minerals may grow so large that they become massive (the size ranges from a few centimetres to several metres). Porphyritic textures develop when conditions during cooling of a magma change relatively quickly.
What does porphyritic texture indicate about an igneous rock?
What is porphyritic texture What sequence of events produces porphyritic texture in rocks?
Porphyritic rocks are formed when a column of rising magma is cooled in two stages. In the first stage, the magma is cooled slowly deep in the crust, creating the large crystal grains, with a diameter of 2mm or more.
