Search results
Results From The WOW.Com Content Network
Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained ( aphanitic ) or glassy .
Flow banding is a geological term to describe bands or layers that can sometimes be seen in rock that formed from magma (molten rock). [ 1 ] Flow banding is caused by friction of the viscous magma that is in contact with a solid rock interface, usually the wall rock to an intrusive chamber or, if the magma is erupted, the surface of the Earth ...
Acidic rock or acid rock refers to the chemical composition of igneous rocks that has 63% wt% SiO 2 content. [1] Rocks described as acidic usually contain more than 20% of free quartz. [2] Typical acidic rocks are granite or rhyolite. The term is used in chemical classification of igneous rock based on the content of silica (SiO 2).
When extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals. The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite.
Trachyte – Extrusive igneous rock – A silica-undersaturated volcanic rock; essentially a feldspathoid-bearing rhyolite; Troctolite – Igneous rock – A plutonic ultramafic rock containing olivine, pyroxene and plagioclase; Trondhjemite – Light-colored intrusive igneous rock – A form of tonalite where plagioclase-group feldspar is ...
"Imperial Porphyry" from the Red Sea Mountains of Egypt A waterworn cobble of porphyry Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm (0.39 in). Porphyry (/ ˈ p ɔːr f ə r i / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.
Comendite is a hard, peralkaline igneous rock, a type of light blue grey rhyolite. [1] Phenocrysts are sodic sanidine with minor albite and bipyramidal quartz. [2] The blue colour is caused by very small crystals of riebeckite or arfvedsonite. [3] The 1903 eruption of Changbaishan volcano in northeast China erupted comendite pumice. [4]
Native American. Native Americans once traveled great distances to Mt. Kineo to acquire its rhyolite rock. This rhyolite is evidence of an igneous (volcanic) phase although the mountain formations also contain slate and sandstone demonstrating sedimentary and metaphoric history as well.