What is aphanitic igneous texture?
Aphanitic – This texture describes very fine grained rock where individual crystals can be seen only with the aid of a microscope, i.e. the rock is mostly groundmass. An aphanitic texture is developed when magma is erupted at the Earth’s surface and cools too quickly for large crystals to grow.
What is aphanitic form?
Aphanitic (a = not, phaner = visible) rocks in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth’ surface. Because extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals.
What is an aphanitic igneous rock?
aphanitic; from Ancient Greek αφανης (aphanḗs) ‘invisible’) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye).
How are phaneritic and aphanitic textures different?
APHANITIC TEXTURE – Igneous rocks that form on the earth’s surface have very fine-grained texture because the crystals are too small to see without magnification. PHANERITIC TEXTURE – Igneous rocks with large, visible crystals because the rock formed slowly in an underground magma chamber.
How is aphanitic formed?
Aphanitic rock is igneous rock in which the grain or crystalline structure is too fine to be seen by the unaided eye. Such rock is formed when the material solidifies at or near the surface so that the cooling is rather rapid. Basalt from surface lava flow often exhibits an aphanitic texture.
What does Aphanitic texture look like?
Aphanitic texture consists of small crystals that cannot be seen by the eye with or hand lens. The entire rock is made up of small crystals, which are generally less than 1/2 mm in size. This texture results from rapid cooling in volcanic or hypabyssal (shallow subsurface) environments.
What is texture describe the Inequigranular texture of igneous rock in detail?
Inequigranular texture (i) Porphyritic texture : When an igneous rock contains large crystals some minerals set in a matrix which is much finer grained or even glassy, the texture is called “Porphyritic”. The large crystals are called “Phenocrysts” and fine grained material is called “groundmass”.
What is the composition of aphanitic?
Aphanitic, extrusive, igneous rocks therefore have coarse-grained, intrusive counterparts with the same chemical and mineral composition. Both rock types are composed mainly of the silicate minerals quartz and orthoclase feldspar , but the crystals in the rhyolite are too small to see without a microscope.
How do Aphanitic rocks differ from phaneritic rocks?
In aphanitic rocks, the crystals are large enough to be identified with the naked eye, while in phaneritic rocks they are not. Phaneritic rocks cool slowly, and therefore have small crystals, while aphanitic rocks have large crystals and cool quickly.
What is the difference between aphanitic and fine grained?
Crystalline rocks with mineral grains that cannot be distinguished from one another without magnification have an aphanitic igneous texture. Intrusive igneous rocks thus have coarse-grained, or phaneritic, textures with visible crystals, and extrusive igneous rocks have fine-grained, or aphanitic, texture.
What is another term for aphanitic?
dictionary aphanitic. aphanitic rocks are also called volcanic rocks.
What does the texture of igneous rocks describe?
The texture of an igneous rock (fine-grained vs coarse-grained) is dependent on the rate of cooling of the melt: slow cooling allows large crystals to form, fast cooling yields small crystals.
What are the types of texture?
There are probably thousands of texture types, but in general they fall under the broad categories of rough and smooth. Smooth textures include slick, silky, soft and slimy. Rough textures are more varied and include bumpy, scaly, coarse, sandy and rocky.
Is coarse-grained an aphanitic?
Coarse grain varieties (with mineral grains large enough to see without a magnifying glass) are called phaneritic. Granite and gabbro are examples of phaneritic igneous rocks. Fine grained rocks, where the individual grains are too small to see, are called aphanitic. The most common glassy rock is obsidian.
What does aphanitic mean?
Definition of aphanitic. i. Said of the texture of an igneous rock in which the crystalline components are not distinguishable by the unaided eye; also said of a rock or a groundmass exhibiting such texture.
Is the aphanitic or fine-grained equivalent of gabbro.?
Basalt is the aphanitic or fine-grained equivalent of gabbro. True Plutonic rocks are intrusive and generally consist of mineral grains coarse enough to be readily visible in a hand sample.