What is the difference between phaneritic and porphyritic rocks?
What is the difference between phaneritic and porphyritic rocks?
Phaneritic: any coarse-grained igneous rock, often intrusive, usually formed as a result of a longer cooling history (ex. granite, gabbro). Porphyritic: an igneous rock with one mineral (called the phenocryst) exhibiting a grain size larger than the remainder of the minerals (called the groundmass).
What is an aphanitic igneous rock?
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.
What is the difference between porphyritic and vesicular rocks?
Porphyritic rocks contain mineral crystals of various sizes. Some grains are distinctly larger than others. Porphyritic rocks, like this one, have mineral grains of very different sizes. Vesicular texture refers to volcanic rocks that contain holes called vesicles that were formed by gas bubbles in lava.
What is an aphanitic rock?
rocks. In rock: Classification by grain or crystal size. Aphanitic is a descriptive term for small crystals, and phaneritic for larger ones. Very coarse crystals (those larger than 3 centimetres, or 1.2 inches) are termed pegmatitic.
What is aphanitic and phaneritic?
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.
What is aphanitic 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 are porphyritic rocks?
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.
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.