What does porphyritic basalt look like?
Porphyrite or porphyritic basalt is characterized by obvious crystals, usually of plagioclase, which is often white or tan in color. These crystals are typically interpreted as phases that formed before eruption, where magma was being stored (a “Magma Chamber).
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. Hence, rhyolite and basalt as fine-grained volcanic rocks are porphyritic and granite, syenite, etc. as coarse-grained plutonic rocks are porphyraceous.
What texture is porphyritic basalt?
Porphyritic Basalt
| Type | Igneous Rock |
|---|---|
| Texture | Porphyritic |
| Origin | Extrusive/Volcanic |
| Chemical Composition | Mafic |
| Color | Dark Gray to Black |
What type of rock is porphyritic basalt?
igneous rock
Porphyritic basalt is a mafic igneous rock having phenocrysts and an aphanitic groundmass. The phenocrysts are calcic plagioclase feldspar (light gray in the photo below). The finely crystalline groundmass is principally a mixture of sodic plagioclase feldspar and pyroxene.
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.
What is a porphyritic texture?
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 rest of the smaller mineral grains are called the groundmass. Porphyritic textures are found in rocks with both coarse- and fine-grained groundmasses.
Where are porphyritic rocks 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.
What causes porphyritic rocks?
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 minerals are in porphyritic rocks?
Pitchstone porphyry (vitrophyre) consists of a glassy base (groundmass) enclosing abundant large crystals (phenocrysts) of such minerals as quartz, alkali feldspar, and plagioclase, as well as fewer crystals of pyroxene or hornblende.
What does porphyritic texture look like?
Porphyritic – This texture describes a rock that has well-formed crystals visible to the naked eye, called phenocrysts, set in a very fine grained or glassy matrix, called the groundmass. This texture is characteristic of most volcanic rocks.
Is porphyritic texture intrusive or extrusive?
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 rock would be porphyritic?
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 clearly much bigger than the rest, as in a porphyritic granite. Most types of igneous rocks may display some degree of porphyritic texture.
What igneous rocks are porphyritic?
Andesite is an extrusive igneous rock that has a porphyritic texture. This rock is formed from molten magma, which has medium viscosity.
What are the properties of basalt?
There are various physical properties of Basalt like Hardness, Grain Size, Fracture, Streak, Porosity, Luster, Strength etc which defines it.
What are the characteristics of basalt?
Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill.