What is porphyritic andesite?

Description. Andesite-porphyry is a porphyry with andesitic chemism. The term “porphyry” is used for igneous rock composed of large, conspicuous crystals (phenocrysts) and a fine grained to glassy groundmass (matrix) in which the phenocrysts are embedded.

How is porphyritic andesite formed?

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.

What kind of rock is porphyritic andesite?

Porphyritic Andesite

What is porphyritic andesite made of?

Andesite most commonly denotes fine-grained, usually porphyritic rocks; in composition these correspond roughly to the intrusive igneous rock diorite and consist essentially of andesine (a plagioclase feldspar) and one or more ferromagnesian minerals, such as pyroxene or biotite.

Why is andesite porphyritic?

Andesite is usually porphyritic, containing larger crystals (phenocrysts) of plagioclase formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained matrix. Phenocrysts of pyroxene or hornblende are also common.

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.

Where is porphyritic andesite formed?

subduction zones

Where Does Andesite Form? Andesite and diorite are common rocks of the continental crust above subduction zones. They generally form after an oceanic plate melts during its descent into the subduction zone to produce a source of magma.

How does a porphyritic texture form?

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.

What is a porphyritic granite?

Granite (porphyritic); Shap, Cumbria. In terms of its mineral content this is a typical granite, consisting of pink potassium feldspar, cream sodium feldspar (plagioclase), grey quartz and black biotite mica.

What is porphyritic rhyolite?

Most rhyolites are porphyritic, indicating that crystallization began prior to extrusion. Crystallization may sometimes have begun while the magma was deeply buried; in such cases, the rock may consist principally of well-developed, large, single crystals (phenocrysts) at the time of extrusion.

What type of rock is porphyritic rhyolite?

Porphyritic Rhyolite

How do you identify porphyritic rocks?

Porphyritic igneous rocks have coarse crystals in a fine background. Crystals are two to three times size of the matrix, and less than 10% of rock is crystals.

Where is porphyritic rhyolite found?

Some of the best-known examples of rhyolite can be found in the Yellowstone Park region and in the southwestern United States. Many of the rocks in those areas formed approximately 600,000 years ago through a series of massive volcanic eruptions.

Is porphyritic rhyolite felsic?

Most rhyolites are light gray to pinkish in color, but red or even black rhyolites are not rare. Most rhyolites are porphyritic and are identified by the quartz phenocrysts and white to salmon K-feldspar phenocrysts.

What type of rock is scoria?

pyroclastic igneous rock

scoria, heavy, dark-coloured, glassy, pyroclastic igneous rock that contains many vesicles (bubblelike cavities).

What is andesite made of?

Andesite is a gray to black volcanic rock with between about 52 and 63 weight percent silica (SiO2). Andesites contain crystals composed primarily of plagioclase feldspar and one or more of the minerals pyroxene (clinopyroxene and orthopyroxene) and lesser amounts of hornblende.

What andesite is used for?

Uses – can be used as aggregate, fill etc. in the construction and roading industries (often not ideal for concrete aggregate because of high silica content).

What is the most common mineral in andesite?

andesine

The primary ingredient of most andesites is andesine, a feldspar of the plagioclase series. Smaller amounts of quartz or minerals rich in iron and magnesium such as olivine , pyroxene, biotite, or hornblende are also present.

Is andesite hard or soft?

The hardness of andesite rocks on the Moh scale is 7.

Why is andesite used for construction?

Andesites are mostly found along continental margins where subduction of ocean tectonic plate. Andesite stones are more durable than calcium rocks and can be much more easy to handle than other volcanic rocks.

Is andesite plutonic or volcanic?

Main types of igneous rocks

What is the specific gravity of andesite?

Specific gravities for minerals and other materials.

What is the specific gravity of feldspar?

about 2.6

Feldspars have a hardness of 6, have a smooth, glassy or pearly luster, and show good cleavages along two planes at nearly right angles to each other. Specific gravity is about 2.6.

How do you calculate specific gravity?

Calculating Specific Gravity



Specific gravity is determined by dividing the density of a material by the density of water at 4 degrees Celsius. For the calculation, the density of the material and that of the water must be expressed in the same units.