Modern petrology defnes a granulite sensuo stricto as a coarse grained, high-grade metamorphic rock composed primarily of pyroxene, plagioclase feldspar and accessory garnet, oxide and amphibole. Granulite is of mafic comosition and may have had a protolith derived from basalt or some intrusive mafic or ultramafic rock. Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... The Garnet group of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. ... An oxide is a chemical compound of oxygen with other chemical elements. ... For the logical fallacy, see Amphibology. ... Protolith refers to the precursor rock of a given lithology. ... Basalt Basalt is an extrusive igneous rock, sometimes porphyritic, and is often both fine-grained and dense. ... In geology, mafic minerals are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Ultramafic rocks are igneous rocks with very low silica content (less than 45%) and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ...

Granulite facies metamorphism gains its name from the mafic granulite which has a particular metamorphic mineral assemblage and characterises the pressure and temperature envelope of the facies.

In common usage, however, granulite sensuo lato refers to any metamorphic rock of any composition which has been metamorphosed to granulite facies. Because the protoliths of felsic and intermediate granulites are difficult to identify, if not usually utterly impossible, the term granulite is used to describe them, and is widely accepted. Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements, such as silica, oxygen, aluminium, sodium, and potassium. ...

Granulite s.l. textures are routinely coarse grained, equigranular to granoblastic. Often, orthogranulites (mafic granulites derived from basalts) may preserve original porphyritic texture as a porphyroblastic texture. This is rare, because complete re-equilibration of the mineral assemblage is favoured at the high temperatures associated with granulite facies metamorphism. (For other meanings of Porphyr, see Porphyry) The baptismal font in the Cathedral of Magdeburg is made of rose porphyry from a site near Assuan, Egypt Porphyry is a very hard red, green or purple igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a...

Formation

Granulites s.l. form only in the deep crust below 30Km, and only in rocks which do not undergo partial melting (see migmatite). Thus, most granulites are dry, because presence of water would promote partial melting. Granulites are rarely preserved during uplift of the deep metamorphic complexes, because of retrograde metamorphic reactions. Generally granulite s.s. will retrogress toward amphibolite or even chlorite assemblages if water exists in sufficent quantities. Thus, preserved granulite terranes have generally remained dry during uplift and retrograde metamorphic opportunities. Migmatite is a rock in the frontier between igneous and metamorphic rocks. ... Amphibolite is a gouping of rocks composed mainly of amphibole (as hornblende) and plagioclase feldspars, with little or no quartz. ...

Interpretation

Interpreting granulites is highly difficult even for trained petrologists, as the full suite of structural geology tools and geochemistry must be brought to bear on these rocks, since most original textures are completely obliterated by the metamorphic reactions. The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earths chemical components in time and space, and their interaction with...

See also

• Migmatite and granite origin
• Metamorphic rocks
• Metamorphic facies

Migmatite is a rock in the frontier between igneous and metamorphic rocks. ... Quarrying granite for the Mormon Temple, Utah Territory. ... The term Metamorphic can be associated with a number of meanings:- Metamorphic rock The term for rocks that have been transformed by extreme heat and pressure. ...

1911 Definition

Granulite (Latin granulum, "a little grain") is a name used by petrographers to designate two distinct classes of rocks. According to the terminology of the French school it signifies a granite in which both kinds of mica (muscovite and biotite) occur, and corresponds to the German Granit, or to the English muscovite biotite granite. This application has not been accepted generally. To the German petrologists granulite means a more or less banded fine-grained metamorphic rock, consisting mainly of quartz and feldspar in very small irregular crystals and usually also containing a fair number of minute, rounded, pale-red garnets. Among English and American geologists the term is generally employed in this sense. Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. ... Sedimentary, volcanic, plutonic, metamorphic rock types of North America. ... Quarrying granite for the Mormon Temple, Utah Territory. ... rock with mica Mica sheet mica flakes The mica group of minerals includes several closely related materials having highly perfect basal cleavage. ... The English language is a West Germanic language that originates in England. ... Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form (from the Greek words meta, change, and morphe, form). The protolith is subjected to extreme heat (greater than 150 degrees Celsius) and pressure causing... Quartz is the most abundant mineral in the Earths continental crust. ... Feldspar is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... The Garnet group of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. ... A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth. ...

The granulites are very closely allied to the gneisses, as they consist of nearly the same minerals, but they are finer-grained, have usually less perfect foliation, are more frequently garnetiferous, and have some special features of microscopic structure. In the rocks of this group the minerals, as seen in a microscopic slide, occur as small rounded grains forming a closely-fitted mosaic. The individual crystals never have perfect form, and indeed traces of it area rare. In some granulites they interlock, with irregular borders; in others they have been drawn out and flattened into tapering lenticles by crushing. In most cases they are somewhat rounded with smaller grains between the larger. This is especially true of the quartz and feldspar which are the predominant minerals; mica always appears as flat scales (irregular or rounded but not hexagonal). Both muscovite and biotite may be present and vary considerably in abundance; very commonly they have their flat sides parallel and give the rock a rudimentary schistosity, and they may be aggregated into bands in which case the granulites are indistinguishable from certain varieties of gneiss. The garnets are very generally larger than the above-mentioned ingredients, and easily visible with the eye as pink spots on the broken surfaces of the rock. They usually are filled with enclosed grains of the other minerals. Banded gneiss with dike of granite orthogneiss Gneiss is a common and widely distributed type of rock formed by high grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. ... This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band). ... Categories: Mineral stubs | Metamorphic rocks ...

The feldspar of the granulites is mostly orthoclase or cryptoperthite; microcline, oligoclase and albite are also common. Basic feldspars occur only rarely. Among accessory minerals, in addition to apatite, zircon, and iron oxides, the following may be mentioned: hornblende (not common), riebeckite (rare), epidote and zoisite, calcite, sphene, andalusite, sillimanite, kyanite, hercynite (a green spinel), rutile, orthite and tourmaline. Though occasionally we may find larger grains of feldspar, quartz or epidote, it is more characteristic of these rocks that all the minerals are in small, nearly uniform, imperfectly shaped individuals. Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Apatite is a group of minerals, usually referring to: hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal lattice. ... Zircon is a mineral belonging to the group of nesosilicates. ... Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... Riebeckite is a sodium-rich member of the amphibole group of minerals, chemical formula Na2(Fe,Mg)5Si8O22(OH)2. ... Epidote is a calcium aluminium iron sorosilicate mineral, Ca2(Al, Fe)3(SiO4)3(OH), crystallizing in the monoclinic system. ... Zoisite is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. ... Calcite from Brushy Creek Mine, Missouri, USA. The carbonate mineral calcite is a calcium carbonate corresponding to the formula CaCO3 and is one of the most widely distributed minerals on the Earths surface. ... Titanite or sphene is a calcium titanium nesosilicate mineral, CaTiSiO5. ... Andalusite-cordierite schist (Large brown crystals are Andalusite Andalusite is an alumino-silicate mineral with the chemical formula Al2SiO5. ... Sillimanite: Biotite gneiss (Mesozoic and Paleozoic) Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. ... Kyanite The mineral kyanite is an aluminium silicate of the sillimanite group (along with andalusite and sillimanite), also called alumino-silicate. ... Emery (also known as iron spinel and hercynite) is a common impure variety of the mineral corundum. ... Rutile in trellis texture characteristic of secondary rutile. ... Allanite is a silicate containing a large amount of cerium. ... The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. ...

On account of the minuteness with which it has been described and the important controversies on points of theoretical geology which have arisen regarding it, the granulite district of Saxony (in the area of Rosswein and Penig) in Germany may be considered the typical region for rocks of this group. It should be remembered that though granulites are probably the commonest rocks of this country, they are mingled with granites, gneisses, gabbros, amphibolites, mica schists and many other petrographical types. All of these rocks show more-or-less metamorphism either of a thermal character or due to pressure and crushing. The granites pass into gneiss and granulite; the gabbros into flaser gabbro and amphibolite; the slates often contain andalusite or chiastolite, and show transitions to mica schists. At one time these rocks were regarded as Archean gneisses of a special type. Johannes Georg Lehmann propounded the hypothesis that their present state was due principally to crushing acting on them in a solid condition, grinding them down and breaking up their minerals, while the pressure to which they were subjected welded them together into coherent rock. It is now believed, however, that they are comparatively recent and include sedimentary rocks, partly of Palaeozoic age, and intrusive masses which may be nearly massive or may have gneissose, flaser or granulitic structures. These have been developed largely by the injection of semi-consolidated highly viscous intrusions, and the varieties of texture are original or were produced very shortly after the crystallization of the rocks. Meanwhile, however, Lehmanns advocacy of post-consolidation crushing as a factor in the development of granulites has been so successful that the terms granulitization and granulitic structures are widely employed to indicate the results of dynamometamorphism acting on rocks at a period long after their solidification. With an area of 18,413 km² and a population of 4. ... Gabbro Gabbro is a dark, coarse-grained, intrusive igneous rock that is chemichly equivalent to basalt. ... Amphibolite is a gouping of rocks composed mainly of amphibole (as hornblende) and plagioclase feldspars, with little or no quartz. ... Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. ... Slate Slate is a fine-grained, homogeneous, metamorphic rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). ... The mineral chiastolite is a variety of Andalusite with the chemical composition Al2OSiO4. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... The Palaeozoic is a major division of the geologic timescale, one of four geologic eras. ... Pluton redirects here. ... The pitch drop experiment at the University of Queensland. ...

The Saxon granulites are apparently for the most part igneous and correspond in composition to granites and porphyries. There are, however, many granulites which undoubtedly were originally sediments (arkoses, grits and sandstones). A large part of the highlands of Scotland consists of paragranulites of this kind, which have received the group name of Moine gneisses. (For other meanings of Porphyr, see Porphyry) Porphyry is a very hard igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ... Arkose is a kind of sandstone combining of quartz and with large amounts of feldspar. ... Sandstone near Stadtroda, Germany Sandstone is an sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. ... ...

Along with the typical acid granulites above described, in Saxony, India, Scotland and other countries there occur dark-colored basic granulites (trap granulites). These are fine-grained rocks, not usually banded, nearly black in color with small red spots of garnet. Their essential minerals are pyroxene, plagioclase and garnet: chemically they resemble the gabbros. Green augite and hypersthene form a considerable part of these rocks, they may contain also biotite, hornblende and quartz. Around the garnets there is often a radial grouping of small grains of pyroxene and hornblende in a clear matrix of feldspar: these centric structures are frequent in granulites. The rocks of this group accompany gabbro and serpentine, but the exact conditions under which they are formed and the significance of their structures is not very clearly understood. An acid (from Arabic Azait meaning oil, often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... Hypersthene is a common rock-forming mineral belonging to the group of orthorhombic pyroxenes. ... Serpentine Serpentine is a group of common rock-forming hydrous magnesium iron phyllosilicate ((Mg,Fe)3Si2O5(OH)4) minerals; it is also often rich in other metal ores, including chromium, manganese, cobalt and nickel. ...

References

• This article incorporates text from the 1911 Encyclopædia Britannica, a publication in the public domain.