What is amygdaloidal structure?
Definition of amygdaloidal : of, being, or containing small cavities in igneous rock that are filled with deposits of different minerals (such as chalcedony)
What is amygdaloidal rock?
This is a basalt, a dark coloured volcanic rock formed from a magma of basic composition erupted on the Earth’s surface. Filled cavities in lavas are called amygdales, and a rock full of them can be called amygdaloidal. The amygdales are usually white in colour.
What does vesicular mean 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 is an Amygdule and how does one form?
amygdule, secondary deposit of minerals found in a rounded, elongated, or almond-shaped cavity in igneous rock. The cavities (vesicles) were created by the expansion of gas bubbles or steam within lava. Some amygdules consist partially of lava, which indicates their formation during solidification of the rock.
What are the amygdales?
Amygdules or amygdales (/əˈmɪɡdjuːlz, -deɪlz/) form when the vesicles (pores from gas bubbles in lava) of a volcanic rock or other extrusive igneous rock are infilled with a secondary mineral, such as calcite, quartz, chlorite, or one of the zeolites. Rocks containing amygdules can be described as amygdaloidal.
What is phaneritic and aphanitic?
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 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 the difference between a sill and a dike?
A sill is a concordant intrusive sheet, meaning that a sill does not cut across preexisting rock beds. In contrast, a dike is a discordant intrusive sheet, which does cut across older rocks. Sills are fed by dikes, except in unusual locations where they form in nearly vertical beds attached directly to a magma source.
How is porphyry formed?
The porphyry deposits are formed by differentiation and cooling of a column of rising magma in stages. The different stages of cooling create porphyritic textures in intrusive as well as in subvolcanic rocks.
What is a phenocrysts in geology?
A relatively large crystal embedded in a finer-grained or glassy igneous rock. The presence of phenocrysts gives the rock a porphyritic texture (see illustration). Phenocrysts are represented most commonly by feldspar, quartz, biotite, hornblende, pyroxene and olivine.
Is quartz an Aphanitic?
Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass, or matrix. They consist essentially of very small crystals of minerals such as plagioclase feldspar, with hornblende or augite, and may contain also biotite, quartz, and orthoclase.
What is amygdules in geology?
Amygdules or amygdales ( / əˈmɪɡ.djulz, – deɪlz /) form when the vesicles (pores from gas bubbles in lava) of a volcanic rock or other extrusive igneous rock are infilled with a secondary mineral, such as calcite, quartz, chlorite, or one of the zeolites.
What is amygdaloid rock?
Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Rocks containing amygdules can be described as amygdaloidal. Melting of pre-existing rock. Compare metatexis, diatexis, and syntexis.
What is the origin of the word amygdale?
The word is derived from the Latin word amygdala, meaning “almond tree”, and the Greek word αμυγδαλή, meaning “almond” – reflecting the typical shape of an infilled vesicle. Amygdule is more common in American usage, while amygdale is more common in British usage.
What is the meaning of amygdaloidal?
Amygdules may often be concentrically zoned. Rocks containing amygdules can be described as amygdaloidal . The word is derived from the Latin word amygdala, meaning “almond tree”, and the Greek word αμυγδαλή, meaning “almond” – reflecting the typical shape of an infilled vesicle.