Igneous rocks are rocks formed from the crystallization of a liquid (molten rock). Igneous rocks may be divided into three categories. Intrusive or plutonic rocks .
Full Answer. Gabbro is a dark and coarsegrained rock that's considered mafic instead of felsic. This means it is made of minerals made largely of iron and magnesium, such as olivine. It is used as a facing stone for buildings and can be dark gray, brown or green. .
Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy. Basalt is a very common extrusive igneous rock. Basalt is the dominant rock in Earth's upper oceanic crust. Black lava rocks seen at famous volcanoes such as Mt. Kilauea in Hawaii and Mt. Etna in Sicily are composed of basalt. Basalt has a mafic ...
As mentioned above, intrusive igneous rocks, such as granite have large, individual crystals visible to the naked eye. The textural term used to describe a rock with large crystals is coarsegrained. In contrast, finegrained rocks, such as basalt, are igneous rocks that have crystals too fine to see with the naked eye.
Dec 24, 2016· Mafic and felsic are terms to describe, both visually and chemically, the silica content of an igneous rock. Felsic rocks have a higher silica content (65% to 75%), so they are generally harder, lighter in color, are enriched in elements such as s...
Gabbro – black, coarsegrained, intrusive igneous rock composed of calcic fspars and pyroxene Diorite – coarsegrained, dark, intrusive, intermediate igneous rock, rich in plagioclase and having little quartz Pumice – A form of volcanic glass, usually felsic composition, filled with holes from the escape of gas
Common Minerals in Igneous Rocks The mineral samples in this section are generally pure mineral specimens. Such pure mineral samples are not commonly found in the wild, but they still illustrate the basic properties displayed by their smaller counterparts in igneous, sedimentary, and metamorphic rocks.
GY303 Igneous Metamorphic Petrology Lab Phaneritic Intermediate to Mafic Igneous Rocks Identification. Intermediate to Mafic Minerals • Ca‐Plagioclase: same as Na‐Plagbut increasing anorthite (Ca) content changes color to dark gray or black. 2 ... • Accessories: spinel, magnetite, pyrite, calcite, ...
Mafic is a term used by geologists to describe igneous rocks and minerals. This lesson will examine the definition of this term and how to relates to earth processes.
Dec 05, 2017· Gabbro is an example of a mafic rock. In geology, mafic is a term which describes an igneous rock or a silicate mineral rich in iron and magnesium. The term mafic is a combination of the words "magnesium" and "ferric." The majority of mafic minerals are dark green or greenish black and are medium to coarsegrained.
Igneous Rocks and Plate Tectonics • Over geologic time these processes first created oceanic crust from ultramafic mantle rocks. In turn, the mafic oceanic crust created felsic continental crust from partial melting of hydrated basalt. Continental crust is less than 1% of earth's mass, so there isn't a lot of felsic material in the earth.
Igneous rocks are two thirds dark minerals and ultramafic rocks are completed made of dark minerals. In broad terms mafic and ultramafic magmas crystallize at higher temperatures than felsic rocks and are more fluid. The majority of copper nickel massive sulfide and chrome platinum group metal deposits developed in large intrusions that are made up of layers of alternating mafic and ultramafic ...
Porphyritic rock is and igneous rocks that contains two distinct crystal sizes. These distinctly different crystal sizes were produced by different cooling of the liquid rock. Large crystals form slowly beneath the surface of the Earth and small crystals form when rapid cooling takes place (normally at or .
One of the several schemes based on chemical composition divides igneous rocks into four categories according to silica (silicon dioxide, SiO2) content: (1) Rocks containing more than 66% silica are silicic . (2) Rocks containing 52–66% silica are classified as intermediate. (3) .
Aug 17, 2013· What physical processes contribute to the weathering of rock and why might you expect mafic igneous rocks to weather at a faster rate than felsic igneous rocks? Weathering is the physical disintegration and chemical decomposition of rocks into soil, loose clasts, dissolved chemical components (ions), and solid chemical residues.