Obsidian, igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite.
Explosive eruptions are favored by high gas content & high viscosity magmas (andesitic to rhyolitic magmas). The explosive bursting of bubbles fragments the magma into clots of liquid that cool as they fall through the air.
Rhyolite rocks have a hardness of 6 according to Mohs scale of hardness. It is sometimes used as crushed stone when other better materials are not available.
Rhyolite is the extrusive equivalent to the plutonic rock type granite - both form from the same magma. Rhyolite lava flows are very viscous. Due to their high viscosity, they only move through laminar flow along sheer planes that form where gas bubbles concentrate.
Gabbro is a mafic intrusive coarse-grained rock with allotriomorphic texture. Gabbros contain low silicon (no Quartz or Alkali feldspar) and essentially of ferromagnesian minerals and Plagioclase feldspar rich in calcium.
Rhyolite is an extrusive igneous rock having cooled much more rapidly than granite, giving it a glassy appearance.
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.
Porphyry is an igneous, volcanic rock with rhyolitic chemism, composed of large, conspicuous crystals (phenocrysts) and a fine grained to glassy groundmass in which the phenocrysts are embedded.
: a very acid volcanic rock that is the lava form of granite.
Volcanic rock (or lava) that characteristically is light in color, contains 69 or more percent of silica, and is rich in potassium and sodium. Rhyolitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes.
Due to their high content of silica and low iron and magnesium contents, rhyolitic magmas form highly viscous lavas. Some rhyolite is highly vesicular pumice. Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas.
Formation. Porphyry deposits are formed when a column of rising magma is cooled in two stages. In the first stage, the magma is cooled slowly deep in the crust, creating the large crystal grains with a diameter of 2 mm or more.
How did it form? Diorite is a course-grained igneous rock that forms when magma rich in silica cools slowly deep within the Earth's crust.
Extremely common in the Earth's crust, igneous rocks are volcanic and form from molten material. They include not only lava spewed from volcanoes, but also rocks like granite, which are formed by magma that solidifies far underground. Typically, granite makes up large parts of all the continents.
4.33) with relatively large thickness and small propagation due to the high viscosity and low capacity of lava flow. Rhyolite is suitable as aggregate, fill-in construction, building material and road industries, decorative rock in landscaping, cutting tool, abrasive and jewelry. FIGURE 4.33.
Pumice has a porosity of 64–85% by volume and it floats on water, possibly for years, until it is eventually waterlogged and sinks. Scoria differs from pumice in being denser. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in water.
Felsic magma, starting much cooler, generally crystallizes before reaching the surface. Therefore, more basalt than gabbro, and more granite than rhyolite. Another reason is the internal crystalline structure of the silicate minerals.
Clean rhyolite jewelry with a soft dry cloth to preserve polish. Clean quickly if the jewelry becomes soiled, as jaspers can be porous and easily stained.
The main difference between basalt and rhyolite is that basalt usually appears in dark colours, while rhyolite usually appears in light colours. Basalt is an extrusive igneous rock type. Rhyolite is considered as an extrusive volcanic rock that is equivalent to granite.
Rhyolitic magma forms as a result of wet melting of continental crust. Rhyolites are rocks that contain water and minerals that contain water, such as biotite. The continental crust must be heated above the normal geothermal gradient in order to melt.
How was it formed? Diorite formed deep within the Earth's crust from cooling magma that never made it to the surface. It usually occurs as quite small intrusions often associated with larger intrusions like granite. Slow cooling produces the large crystals.
Scoria. Scoria is an igneous rock with vesicular texture. The vesicles, or holes, in the rock form from bubbles of volcanic gas. Scoria forms the crust of lava flows.
sedimentary carbonate rock
Andesite is a fine-grained igneous rock that forms when the magma is erupted onto the surface and is crystallized quickly. Rhyolite is a felsic extrusive rock and due to its high silica content, rhyolite lava is very viscous and is volcanic equivalent of granite.
geo quiz 6
| Question | Answer |
|---|
| Spreading center volcanism most generally produces rocks that are ________. | basaltic in composition |
| Which kind of eruptive activity is most likely to be highly explosive? | eruptions of big, continental margin, composite cones or stratovolcanoes |
There are three common types of magma which are as follows from high temperature to low temperature: basaltic (50% SiO2); andesitic (60% SiO2); and rhyolitic (70% SiO2). Basaltic magma has a low viscosity whereas rhyolitic magma has a high viscosity. Basaltic eruptions are non-explosive.
Andesite is an extrusive rock intermediate in composition between rhyolite and basalt. Andesite lava is of moderate viscosity and forms thick lava flows and domes. The word andesite is derived from the Andes Mountains in South America, where andesite is common. Andesite is the volcanic equivalent of diorite.
Granite is a light-colored plutonic rock found throughout the continental crust, most commonly in mountainous areas. It consists of coarse grains of quartz (10-50%), potassium feldspar, and sodium feldspar. These minerals make up more than 80% of the rock.
Granitic, or rhyolitic, magmas and andesitic magmas are generated at convergent plate boundaries where the oceanic lithosphere (the outer layer of Earth composed of the crust and upper mantle) is subducted so that its edge is positioned below the edge of the continental plate or another oceanic plate.
The Yellowstone Caldera is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States, sometimes referred to as the Yellowstone Supervolcano. The caldera and most of the park are located in the northwest corner of Wyoming.
