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I believe that porphyritic andesite is formed from volcanic ash and bits and pieces of minerals that eventually become ejected from the volcano. How the andesite becomes porphyritic is that it formed inside the volcano before being blown out of along with the magma and hot gases. You can find silver and gold specs as well as a few other metals encased by a smooth texture of solidifyed ash. Lee Durst (WVC 08)
Porphyritic rocks form when magma slowly cools beneath the Earth's surface, allowing large crystals (phenocrysts) to grow within a fine-grained matrix. The phenocrysts are surrounded by a finer-grained groundmass, resulting in a distinctive texture.
A porophyritic rock is igneous by classification. Porphyritic rocks begin to form below the surface when minerals with a higher melting temperature crystallize and are carried to or near the surface where the surrounding minerals with lower melting temperatures crystallize, resulting in a porphyritic texture.
Porphyritic textures are formed when magma begins to cool while it is still underground. Minerals that crystallize at higher temps will start to separate out and form crystals. As the magma cools, these crystals get larger, some other minerals will crystalize and then the magma is erupted. Once the magma is erupted it will cool very quickly resulting in a finer grained matrix. When the magma is erupted, the water that was in the magma is suddenly ejected/expelled which also results in a halt of crystallization.
Porphyry deposits are formed when a column of rising magma is cooled in two stages. In the first stage, the magma is cooled slowly deep in the crust, creating the large crystal grains, with a diameter of 2 mm or more. In the final stage, the magma is cooled rapidly at relatively shallow depth or as it erupts from a volcano, creating small grains that are usually invisible to the unaided eye
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What are the crystal structures in porphyritic rocks?
Porphyritic rocks typically have a porphyritic texture, where large crystals (phenocrysts) are embedded in a finer-grained matrix (groundmass). The crystal structures within porphyritic rocks can vary depending on the minerals present, but common examples include feldspar, quartz, and mica minerals. These minerals can form a variety of crystal structures such as monoclinic, triclinic, or hexagonal depending on their composition and arrangement of atoms.
Which igneous rock cools the fastest glassy aphanitc pegmatic and porphyritic?
Glassy igneous rocks cool the fastest, followed by aphanitic, porphyritic, and then pegmatic igneous rocks. Glassy rocks cool almost instantly because they lack any visible crystal structure, whereas aphanitic rocks have small crystals that form quickly, porphyritic rocks have large and small crystals that form at different rates, and pegmatic rocks have very large crystals that take the longest to cool.
Is porphyritic texture is not a feature of sedimentary rocks?
Correct, porphyritic texture is typically associated with igneous rocks and is not a common feature of sedimentary rocks. It is characterized by larger crystals, known as phenocrysts, surrounded by a fine-grained or glassy matrix. Sedimentary rocks are formed through the accumulation and lithification of sediments, which do not typically undergo the same crystallization processes as igneous rocks.
Is felsic porphyritic extrusive?
Felsic porphyritic rocks can be extrusive if they are formed from volcanic eruptions. These rocks have a high silica content and typically contain large crystals (phenocrysts) embedded in a fine-grained matrix. Examples of felsic porphyritic extrusive rocks include rhyolite and dacite.
What igneous rocks are both intrusive and extrusive?
The igneous rocks that can be both intrusive and extrusive are known as porphyritic rocks. These rocks form when magma partially cools underground (intrusive) before being erupted onto the Earth's surface where the remaining magma cools quickly (extrusive). This dual cooling process creates distinctive textures in the rock, with larger crystals (phenocrysts) embedded in a finer-grained matrix.
Are sedimentary rocks that form when minerals come out of a solution classified as porphyritic?
No, sedimentary rocks that form from minerals precipitating out of a solution are classified as chemical sedimentary rocks, not porphyritic. Porphyritic rocks typically refer to igneous rocks with larger crystals (phenocrysts) embedded in a fine-grained matrix.
What are porphyritic rocks?
Porphyritic Rocks are rocks that have big and small crystal's like the Igneous Rock "Andesite".
What are rocks containing two different sizes of crystal called?
Such rocks are porphyritic.
What are the crystal structures in porphyritic rocks?
Porphyritic rocks typically have a porphyritic texture, where large crystals (phenocrysts) are embedded in a finer-grained matrix (groundmass). The crystal structures within porphyritic rocks can vary depending on the minerals present, but common examples include feldspar, quartz, and mica minerals. These minerals can form a variety of crystal structures such as monoclinic, triclinic, or hexagonal depending on their composition and arrangement of atoms.
What Mineral alignment in a metamorphic rock usually gives the rock a porphyritic texture?
The alignment of large porphyroblasts in a fine-grained matrix results in a porphyritic texture in metamorphic rocks. This texture is commonly seen in rocks that have undergone regional metamorphism, where minerals like garnet or staurolite form large crystals in a finer-grained background.
Which igneous rock cools the fastest glassy aphanitc pegmatic and porphyritic?
Glassy igneous rocks cool the fastest, followed by aphanitic, porphyritic, and then pegmatic igneous rocks. Glassy rocks cool almost instantly because they lack any visible crystal structure, whereas aphanitic rocks have small crystals that form quickly, porphyritic rocks have large and small crystals that form at different rates, and pegmatic rocks have very large crystals that take the longest to cool.
Is porphyritic texture is not a feature of sedimentary rocks?
Correct, porphyritic texture is typically associated with igneous rocks and is not a common feature of sedimentary rocks. It is characterized by larger crystals, known as phenocrysts, surrounded by a fine-grained or glassy matrix. Sedimentary rocks are formed through the accumulation and lithification of sediments, which do not typically undergo the same crystallization processes as igneous rocks.
Is felsic porphyritic extrusive?
Felsic porphyritic rocks can be extrusive if they are formed from volcanic eruptions. These rocks have a high silica content and typically contain large crystals (phenocrysts) embedded in a fine-grained matrix. Examples of felsic porphyritic extrusive rocks include rhyolite and dacite.
What igneous rocks are both intrusive and extrusive?
The igneous rocks that can be both intrusive and extrusive are known as porphyritic rocks. These rocks form when magma partially cools underground (intrusive) before being erupted onto the Earth's surface where the remaining magma cools quickly (extrusive). This dual cooling process creates distinctive textures in the rock, with larger crystals (phenocrysts) embedded in a finer-grained matrix.
What is the cooling rate of a porphyritic rock?
The cooling rate of a porphyritic rock can vary depending on the specific conditions during its formation, but generally it is considered to be intermediate. This means that porphyritic rocks cool at a moderate rate, which allows for the formation of both large crystals (phenocrysts) and finer-grained matrix.
3 main groups of igneous rocks?
The three main groups of igneous rocks are intrusive (plutonic), extrusive (volcanic), and hypabyssal rocks. Intrusive rocks form below the Earth's surface from the slow cooling of magma. Extrusive rocks form on the Earth's surface from rapidly cooling lava. Hypabyssal rocks are intermediate rocks that form from magma that solidifies in the crust.
When large masses of magma solidify far below Earths surface they form igneous rocks that have a .?
Coalesced magma bodies are referred to as plutonic rocks, they have a porphyritic texture or larger crystals since elements are allotted more time to segregate to their desired energy environments and precipitate minerals.
