What type of rock is Peralkaline Trachyte?
What type of rock is Peralkaline Trachyte?
A subgroup of the Feldspar Group, poor in calcium, and mostly rich in potassium. A petrological term for Albite-Anorthite Series.
What type of rock is porphyry?
feldspar minerals (A porphyry is an igneous rock containing conspicuous crystals, called phenocrysts, surrounded by a matrix of finer-grained minerals or glass or both.) In most rocks, both alkali and plagioclase feldspars occur as irregularly shaped grains with only a few or no crystal faces. This general absence…
Are porphyritic rocks intrusive?
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. True porphyry according to this interpretation is an intrusive rock.
Is rhyolite porphyry intrusive or extrusive?
rhyolite, extrusive igneous rock that is the volcanic equivalent of granite. Most rhyolites are porphyritic, indicating that crystallization began prior to extrusion.
Is Basalt intrusive or extrusive?
basalt, extrusive igneous (volcanic) rock that is low in silica content, dark in colour, and comparatively rich in iron and magnesium.
What some identifying features of trachyte that make it an igneous rock?
Trachyte (/ˈtreɪkaɪt, ˈtrækaɪt/) is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and alkali metals. It is the volcanic equivalent of syenite.
Is porphyry a sedimentary rock?
“Porphyry” is a diversity of igneous rock consisting of large-grained crystal such as quartz and feldspar scattered in a fine-grained groundmass.
Is basalt porphyry intrusive or extrusive?
Porphyritic Basalt
| Type | Igneous Rock |
|---|---|
| Texture | Porphyritic |
| Origin | Extrusive/Volcanic |
| Chemical Composition | Mafic |
| Color | Dark Gray to Black |
Are porphyritic rocks extrusive?
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 basalt, or phanerites or intrusive rock, with individual crystals of the groundmass easily distinguished with the eye, but one group of crystals …
Is pyroclastic intrusive or extrusive?
Now let us briefly consider textures of tephra or pyroclastic rocks. Like lava flow rocks, these are also extrusive igneous rocks. However, instead of originating from lava that flowed on the earth’s surface, tephra is volcanic material that was hurled through the air during a volcanic eruption.
Can basalt be intrusive?
Intrusive igneous rocks crystallize below Earth’s surface, and the slow cooling that occurs there allows large crystals to form. These rocks include: andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff.
What type of rock is trachyte?
Trachyte is a extrusive igneous rock that light coloured is composed mostly of alkali feldspar with minor amount of dark coloured minerals such as biotite, amphibole, or pyroxene. Trachyte is the volcanic equivalent of rock Syenite.
What is a trachytic texture?
Trachytic texture occurs in alkaline rich rocks; therefore, the vitreous mass of the rocks has a relatively low viscosity. Trachytic texture is especially characteristic of trachytes and rocks similar to trachytes.
What are phenocrysts in Italian trachytes?
Basic varieties of plagioclase, such as labradorite, are known also as phenocrysts in some Italian trachytes. Dark brown varieties of augite and rhombic pyroxene ( hypersthene or bronzite) have been observed but are not common. Apatite, zircon and magnetite are practically always present as accessory minerals.
Is porphyry granitic or porphyritic?
Sometimes it is assumed that porphyry is granitic in composition 1 while other sources claim that composition plays no role whatsoever2. Some authors make a difference between porphyry and porphyritic rock. This is based on field relations. True porphyry according to this interpretation is an intrusive rock.
