What is vesicular in rocks?
Vesicles are the small holes left behind after lava cools and turns into volcanic rock. Vesicles help geologists understand the cooling history of extrusive (volcanic rocks) because lava contains large amounts of dissolved gases that are released as the lava hardens.
What does vesicular texture indicate?
Vesicular texture refers to volcanic rocks that contain holes called vesicles that were formed by gas bubbles in lava.
What is 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 extra large mineral grains are called phenocrysts.
What is the difference between vesicular structure and amygdaloidal structure?
If the bubbles do not get large enough to pop, they are frozen in the lava as vesicles. Amygdaloids are simply vesicles that have been filled in with a secondary mineral long after the flow cooled. Such secondary minerals are commonly white: quartz, calcite, or zeolite.
What is a good example of a glassy rock?
Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include: andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff.
What is amygdaloidal basalt?
Amygdaloidal basalt. This is a basalt, a dark coloured volcanic rock formed from a magma of basic composition erupted on the Earth’s surface. Magmas generally contain dissolved gas, which can form bubbles in the magma as the pressure is released on eruption. These bubbles can get trapped in the solidified rock.
What is Vug in geology?
1. n. [Geology] A cavity, void or large pore in a rock that is commonly lined with mineral precipitates. Alternate Form: vuggy, vugular. See: mineral, pore, vugular porosity.
What is Amygdaloidal in geology?
Definition of amygdaloidal : of, being, or containing small cavities in igneous rock that are filled with deposits of different minerals (such as chalcedony)
How is glassy texture different from vesicular texture?
Glassy texture refers to a quick/rapid cooling lava that does not have an underlying organized mineral structure visible under a conventional polarized light microscope. Vesicular texture occurs when gases are trapped within a lava flow and minerals crystallize around the gas pocket.
Is obsidian aphanitic or Phaneritic?
Examples of aphanitic igneous rock include basalt, andesite and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass with few or no crystals. Examples include obsidian.