What does a porphyritic texture indicate about an igneous rock?
What does porphyritic texture indicate about the history of an igneous rock? 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. The large crystals are termed phenocrysts while the aphanitic rest of rock is called the groundmass.
What rock would be porphyritic?
Scale box in millimeters. Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all types of igneous rocks can display some degree of porphyritic texture.
What igneous rocks are porphyritic?
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. K-feldspar phenocrysts in this sample.
What does andesite look like?
Andesite is the name of a family of fine-grained, extrusive igneous rocks that are usually light to dark gray in color. They have a mineral composition that is intermediate between granite and basalt. Andesite is a rock typically found in volcanoes above convergent plate boundaries between continental and oceanic plates.
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 is the definition of porphyritic?
Definition of porphyritic 1 : of or relating to porphyry. 2 : having distinct crystals (as of feldspar) in a relatively fine-grained base.
What rocks are porphyritic?
Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all types of igneous rocks can display some degree of porphyritic texture.
What kind of igneous rock has a porphyritic texture?
extrusive igneous rockIgneous Rock Types and Textures. Porphyritic texture -- andesite: This is an extrusive igneous rock. The magma from which it formed cooled slowly for a while deep below the surface (forming the large crystals), then finished cooling very quickly when it was ejected at the surface, forming the fine-grained groundmass.
How is porphyritic texture formed?
A porphyritic texture is developed when magma that has been slowly cooling and crystallising within the Earth's crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly. This texture is characteristic of most volcanic rocks.
Where are porphyritic rocks formed?
Porphyritic textures are found in rocks with both coarse- and fine-grained groundmasses. Because larger grains generally indicate longer cooling rates, the phenocrysts indicate that the magma experienced an initial phase of slow cooling deep underground.
What minerals are in porphyritic?
Porphyritic GraniteTypeIgneous RockMineral CompositionPotassium Feldspar, Quartz, Sodium Plagioclase, Biotite, HornblendeMiscellaneousVery large Potassium Feldspar Phenocrysts in a phaneritic (coarse-grained) groundmassTectonic EnvironmentConvergent Boundary – Intruded into batholiths above Andean-type Subduction Zone4 more rows
What is the difference between phaneritic and porphyritic?
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 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 are the 3 textures of rocks?
Igneous Rock TexturesCOARSE 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)More items...
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.
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.
What is porphyritic basalt?
Porphyritic basalt is an igneous rock, which means it was formed from molten rock or lava, cooling underground and then erupting onto the Earth's surface.
What type of rock is Phaneritic?
igneous rockPhaneritic: 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).
Are Phenocrysts igneous or metamorphic?
igneous rockA phenocryst is a large crystal in an igneous rock. It is a cognate crystal, almost invariably early formed, and is genetically distinct from a xenocryst (Iddings, 1889).
What is vesicular in rocks?
Vesicles are the small holes left behind after lava cools and turns into volcanic rock. Vesicles help geologists understand the cooling history of extrusive (volcanic rocks) because lava contains large amounts of dissolved gases that are released as the lava hardens.