What makes a rock porphyritic?

What makes a rock porphyritic?

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. This texture is exhibited by some volcanic rocks.

What are the large mineral grains in a porphyritic igneous rock called?

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 extra large mineral grains are called phenocrysts.

How do you identify porphyritic rocks?

Rocks are said to be porphyritic if their groundmass is fine-grained ar aphanitic and porphyraceous if their groundmass in visible to the naked eye.

Are porphyritic rocks mafic or felsic?

Porphyritic Textures with Fine-Grained Groundmasses The rocks below cover mafic, intermediate, and felsic compositions (top to bottom). This is a fine-grained basalt with olivine phenocrysts (pale green blobs). This is an andesite with amphibole (hornblende) phenocrysts. This is a porphyritic rhyolite.

Which mineral is commonly found in igneous rocks?

These elements combine within a melt to form silicate minerals, the most common minerals of igneous rocks. These silicate minerals include feldspars (plagioclase feldspar, potassium feldspar), quartz, micas (muscovite, biotite), pyroxenes (augite), amphiboles (hornblende), and olivine.

How do you identify minerals in igneous rocks?

The name of the igneous rock depends on what minerals are present. If there are lots of light-colored minerals and the rock is coarse grained, it is granite. If there are mostly dark-colored minerals and the rock is fine grained, it is basalt.

Where are porphyritic rocks found?

When the ground mass is composed of small crystals of feldspar and quartz, the rock is called granite-porphyry. Both are of the composition of granite, and both are found in the elvan dikes of the tin district in Cornwall. Quartz- porphyry is common in the Porcupine gold camp, Ontario.

What are porphyritic rocks used for?

Thus, “imperial”-grade porphyry was prized for monuments and building projects in Imperial Rome and thereafter. Subsequently, the name was given to any igneous rocks with large crystals. The adjective porphyritic now refers to a certain texture of igneous rock regardless of its chemical and mineralogical composition.

Which minerals would you expect to be the phenocrysts in a porphyritic mafic igneous rock?

A porphyritic igneous rock contains phenocrysts of olivine and calcium-rich plagioclase in an aphanitic groundmass. This is a __________? A porphyritic igneous rock contains phenocrysts of olivine and calcium-rich plagioclase in an phaneritic groundmass.

What igneous rock has a porphyritic texture and an intermediate mineral composition?

Volcanic rocks, especially felsic and intermediate, often have a porphyritic texture characterized by visible crystals floating in a fine-grained groundmass.

How many minerals are common in igneous rocks?

About 200 minerals make up the bulk of most rocks. The feldspar mineral family is the most abundant. Quartz, calcite, and clay minerals are also common. Some minerals are more common in igneous rock (formed under extreme heat and pressure), such as olivine, feldspars, pyroxenes, and micas.

What minerals are in igneous rock?

Feldspars, quartz or feldspathoids, olivines, pyroxenes, amphiboles, and micas are all important minerals in the formation of almost all igneous rocks, and they are basic to the classification of these rocks.

What kind of minerals are found in porphyritic rocks?

It is often assumed that phenocrysts that form the porphyritic texture must be felsic (feldspars (preferably alkali feldspars) or quartz). The green mineral here is olivine. But it does meet the most important and universal characteristics of porphyritic rocks — it is igneous and some minerals are clearly larger than the groundmass.

What kind of texture does a porphyry rock have?

Porphyry. 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.

Where are Phenocrysts found in a porphyritic texture?

Trevor Nace on August 15, 2017 Leave a Comment! A phenocryst is a large crystal that visually stands out compared to the rest of the minerals. Phenocrysts are found in porphyritic textures where large grains are visible in volcanic extrusive rocks.

When do coarse grains develop in a porphyritic rock?

Porphyritic textured rocks contain both a coarse and fine-grained texture. The coarse grains in a porphyritic rock begin to develop as the magma is cooling below the surface of the earth. Following eruption or exposure to

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