What type of rock is rhyodacite?
volcanic rock
Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite.
What is rhyolite porphyry?
Rhyolite is a fine-grained extrusive igneous rock that is mineralogically similar to granite. It chiefly contains orthoclase feldspar and quartz, but may contain lesser amounts of plagioclase feldspar, pyroxenes, biotite, and amphiboles.
How is rhyolite porphyry formed?
Rhyolite usually forms in continental or continent-margin volcanic eruptions where granitic magma reaches the surface. Rhyolite is rarely produced at oceanic eruptions. Rhyolite Porphyry: Several specimens of rhyolite porphyry, each about three inches across.
What is porphyritic rhyodacite?
Porphyritic rhyodacite in the Holocene of California, USA. This rock is in “Chaos Jumbles”, a large landslide deposit (usually mis-referred to as an “avalanche”) near Mt. Lassen (Lassen Peak), a prominent volcano in northern California’s Cascade Range.
Is Rhyodacite mafic or felsic?
The felsic volcanic units are represented by dacite, rhyodacite and rhyolite including quartz porphyry and quartz feldspar porphyry. The felsic rocks have mafic xenoliths at some places (Fig. 2B).
What color is rhyolite porphyry?
Most rhyolites are light gray to pinkish in color, but red or even black rhyolites are not rare. Most rhyolites are porphyritic and are identified by the quartz phenocrysts and white to salmon K-feldspar phenocrysts. The groundmass is aphanitic or even glassy.
Is rhyolite porphyry intrusive or extrusive?
rhyolite, extrusive igneous rock that is the volcanic equivalent of granite. Most rhyolites are porphyritic, indicating that crystallization began prior to extrusion.
What causes porphyry?
Porphyritic rocks are formed when a column of rising magma is cooled in two stages. In the final stage, the magma is cooled rapidly at relatively shallow depth or as it erupts from a volcano, creating small grains that are usually invisible to the unaided eye typically referred to as the ground mass.
What is porphyry used for?
Porphyry is prized for its great compressive strength and exceptional durability. For this reason it is now most commonly used as a paving stone.
What is the mineral content of diorite?
diorite, medium- to coarse-grained intrusive igneous rock that commonly is composed of about two-thirds plagioclase feldspar and one-third dark-coloured minerals, such as hornblende or biotite.
What kind of feldspar is found in rhyodacite?
Rhyodacite then describes a fine-grained igneous rock containing between 20% and 60% quartz and in which plagioclase makes up about two-thirds of the total feldspar content. Such a rock will contain between 69% and 72% silica by weight.
What kind of rock is rhyodacite made of?
Rhyodacite is a high silica rock containing 20% to 60% quartz with the remaining constituents being mostly feldspar. The feldspar is a mix of alkaline feldspar and plagioclase, with plagioclase forming 35% to 65% of the mix. Rhyodacite often exists as explosive pyroclastic volcanic deposits.
Which is intermediate in composition between dacite and rhyolite?
Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid cooling of lava relatively rich in silica and low in alkali metal oxides .
What are the trace accessory minerals of rhyolite?
Trace accessory minerals may also include muscovite, pyroxenes, amphiboles, and oxides. Rhyolite has composition similar to that of granite but with much smaller grains. It is composed of light colour silicates. Generally composition is quartz and plagioclase with less amount of orthoclase, biotite, amphibole, pyroxene and glass.