What is the mineral composition of rhyolite?
Mineral content – groundmass generally of quartz and plagioclase, with lesser amounts of orthoclase, biotite, amphibole ( augite), pyroxene ( hornblende), and glass; phenocrysts of plagioclase and quartz, often with amphibole and / or biotite, sometimes orthoclase.
What is the composition of serpentinite?
The final mineral composition of serpentinite is usually dominated by lizardite, chrysotile, and magnetite. Brucite and antigorite are less commonly present. Lizardite, chrysotile, and antigorite are serpentine minerals.
What is the percentage of each mineral in rhyolite?
Rhyolite, with felsic minerals comprising >20% quartz and alkali feldspar/plagioclase 40-90%.
What is the difference between serpentine and serpentinite?
Firstly, “serpentine” refers to a group of minerals, not a rock. Serpentinite is a metamorphosed version of rocks that make up oceanic crust after they are incorporated into subduction zones (plate boundaries where oceanic plates are thrust under continental plates).
How is rhyolite made?
Rhyolite is a volcanic rock. It is fine-grained because it forms by the rapid cooling of magma, usually when it erupts onto the Earth’s surface. When rhyolite erupts quietly it forms lava flows. Rhyolite forms from magma that contains lots of silica (quartz) and is the fine-grained equivalent of granite.
What is andesitic composition?
Andesite most commonly denotes fine-grained, usually porphyritic rocks; in composition these correspond roughly to the intrusive igneous rock diorite and consist essentially of andesine (a plagioclase feldspar) and one or more ferromagnesian minerals, such as pyroxene or biotite.
How is serpentinite formed?
The serpentinite is formed by the hydrous alteration and low-temperature metamorphic alteration of igneous ultramafic rocks. These rocks are composed of olivine and pyroxene in different ratios to form peridotite and pyroxenite.
Does rhyolite have a mafic composition?
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.
What is serpentinite used for?
Serpentine is used mainly as a decorative stone or for ornamental objects. Serpentine gemstones have been used as a source of magnesium, in asbestos and for personal adornment or sculpture throughout history. Various serpentine minerals have even been used in architecture for thousands of years.
Where are rhyolite formed?
volcanic eruptions
Rhyolite usually forms in continental or continent-margin volcanic eruptions where granitic magma reaches the surface. Rhyolite is rarely produced at oceanic eruptions.
What kind of minerals are found in serpentinite rocks?
Serpentinite is a metamorphic rock that is mostly composed of serpentine group minerals. Serpentine group minerals antigorite, lizardite, and chrysotile are produced by the hydrous alteration of ultramafic rocks.
What makes up the composition of a rhyolite rock?
Rhyolite rocks bear a striking resemblance to granite, due to being classified as felsic rocks, except that rhyolite has a fine-grained texture with phenocrysts, which are small crystals sometimes embedded within the rock. The minerals that make up the composition of this rock are mica, feldspar, quartz, and hornblende.
What is the formula for the mineral serpentine?
Serpentine is not the name of a single mineral. Instead it is a name used for a large group of minerals that fit this generalized formula: (X)2-3(Y)2O5(OH)4. In this formula, X will be one of the following metals: magnesium, iron, nickel, aluminum, zinc, or manganese; and, Y will be silicon, aluminum, or iron.
What makes a serpentinite a brucite or magnetite?
Brucite forms if the precursor rocks are rich in magnesium ( dunite, for example). Magnetite forms if there is enough iron present (pyroxenite). Usually serpentinite contains iron in the form of magnetite which gives dark color to serpentinites.