Search results
Results From The WOW.Com Content Network
The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to the older basic rock class. [9] Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava.
These structures are lighter colored than the host rock and typically range in diameter from 0.05mm to over 5 cm. [1] [2] [3] In 1648, Aldrovandi created the term variolite for aphanitic or fine-grained igneous rocks containing varioles. [4] [5] The weathering of varioles often cause variolites to have a pock-marked appearance.
Serpentinization is a form of low-temperature (0 to ~600 °C) [5] metamorphism of ferromagnesian minerals in mafic and ultramafic rocks, such as dunite, harzburgite, or lherzolite. These are rocks low in silica and composed mostly of olivine ( (Mg 2+ , Fe 2+ ) 2 SiO 4 ), pyroxene ( XY(Si,Al) 2 O 6 ), and chromite (approximately FeCr 2 O 4 ).
Peridotite, a type of ultramafic rock. Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals (dark colored, high magnesium and iron content).
Diorite – Igneous rock type Napoleonite, also known as corsite – Variety of diorite with orbicular structure; Dunite – Ultramafic and ultrabasic rock from Earth's mantle which is made of the mineral olivine; Essexite – Igneous rock type; Foidolite – Igneous rock rich in feldspathoid minerals; Gabbro – Coarse-grained mafic intrusive rock
Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust , or sial , generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams ...
Komatiites are rare rocks; almost all komatiites were formed during the Archaean Eon (4.03–2.5 billion years ago), with few younger (Proterozoic or Phanerozoic) examples known. This restriction in age is thought to be due to cooling of the mantle, which may have been 100–250 °C (212–482 °F) hotter during the Archaean.
A rock with over 90% mafic mineral content will be classified instead as an ultramafic rock. A gabbroic rock with less than 10% mafic mineral content will be classified as an anorthosite. [8] [13] A more detailed classification is based on the relative percentages of plagioclase, pyroxene, hornblende, and olivine. The end members are: [8] [13]