What is the difference between porphyritic and phaneritic?
Phaneritic: any coarse-grained igneous rock, often intrusive, usually formed as a result of a longer cooling history (ex. granite, gabbro). Porphyritic: an igneous rock with one mineral (called the phenocryst) exhibiting a grain size larger than the remainder of the minerals (called the groundmass).
What is the difference between phaneritic and porphyritic grain texture in igneous rocks?
PHANERITIC TEXTURE – Igneous rocks with large, visible crystals because the rock formed slowly in an underground magma chamber. PORPHYRITIC TEXTURE – an igneous rock in which PHENOCRYSTS (large crystals) are surrounded by a fine groundmass (very small crystals).
What distinguishes a porphyritic texture in igneous rocks?
An igneous rock with crystals of distinctly different size (Figure 7.14) is said to have a porphyritic texture, or might be referred to as a porphyry. The larger crystals are called phenocrysts, and the smaller ones are referred to as the groundmass.
How would you describe a porphyritic texture?
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 are the 3 textures of rocks?
Igneous Rock Textures
- COARSE GRAINED TEXTURE (PHANERITIC), mineral grains easily visible (grains several mm in size or larger)
- B) FINE GRAINED TEXTURE (APHANITIC), mineral grains smaller than 1mm (need hand lens or microscope to see minerals)
- C) PORPHYRITIC TEXTURE (MIXED FINE AND COARSE)
What are the 4 different textures of igneous rocks?
Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic.
How are phaneritic rocks formed?
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth’s surface. As magma cools slowly the minerals have time to grow and form large crystals.
What are the differences in the textures of igneous rocks?
Igneous rocks may be simply classified according to their chemical/mineral composition as felsic, intermediate, mafic, and ultramafic, and by texture or grain size: intrusive rocks are course grained (all crystals are visible to the naked eye) while extrusive rocks may be fine-grained (microscopic crystals) or glass ( …
What is an example of porphyritic texture?
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. Examples of porphyritic rocks are: andesite porphyry and rhyolite porphyry.
What causes porphyritic texture?
Porphyritic textures develop when conditions during cooling of a magma change relatively quickly. The earlier formed minerals will have formed slowly and remain as large crystals, whereas, sudden cooling causes the rapid crystallization of the remainder of the melt into a fine grained (aphanitic) matrix.
What is an example of a porphyritic rock?
Examples of porphyritic rocks are: andesite porphyry and rhyolite porphyry. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass with few or no crystals. Examples include obsidian and pumice.
What are the 3 major texture categories?
Thus there are distinct igneous textures, distinct sedimentary texture, and distinct metamorphic textures.
What types of rocks are phaneritic?
igneous rock
Phaneritic rock is igneous rock with large, identifiable crystals of roughly equal size. Such crystals are characteristic of rocks which solidified far below the surface so that the cooling was slow enough to enable the large crystals to grow. Such rocks are termed “intrusive” rocks.
What is another term for phaneritic?
Said of the texture of an igneous rock in which the individual components are distinguishable with the unaided eye, i.e., megascopically crystalline. Also, said of a rock having such texture. Synonym of: macromeritic, phanerocrystalline, phenocrystalline. Compare with: aphanitic.
What is the meaning of porphyritic?
Definition of porphyritic
1 : of or relating to porphyry. 2 : having distinct crystals (as of feldspar) in a relatively fine-grained base.
How do you know if you have porphyritic?
Porphyrite or porphyritic basalt is characterized by obvious crystals, usually of plagioclase, which is often white or tan in color. These crystals are typically interpreted as phases that formed before eruption, where magma was being stored (a “Magma Chamber).
What is the difference between porphyritic and pegmatitic textures?
If there were two stages of cooling (slow then fast), the texture may be porphyritic (large crystals in a matrix of smaller crystals). If water was present during cooling, the texture may be pegmatitic (very large crystals). Magma intrudes into country rock by pushing it aside or melting through it.
What is meant by porphyritic?
What is the meaning of phaneritic?
[ făn′ə-rĭt′ĭk ] Of or relating to an igneous rock in which the crystals are so coarse that individual minerals can be distinguished with the naked eye. Phaneritic rocks are intrusive rocks that cooled slowly enough to allow significant crystal growth. Compare aphanitic.