Greywacke (German grauwacke, signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly-sorted, angular grains of quartz, feldspar, and small rock fragments set in a compact, clay-fine matrix. It is a texturally-immature sedimentary rock generally found in Palaeozoic strata. The larger grains can be sand-to-gravel-sized, and matrix materials generally constitute more than 15% of the rock by volume. Red Sandstone in Wyoming Layered sandstone Sandstone is an arenaceous sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. ... For other uses of this word, see Quartz (disambiguation). ... 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. ... 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. ... Interstate road cut through limestone and shale strata in eastern Tennessee In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. ...

The origin of greywacke is problematic, since, according to the normal laws of sedimentation, gravel, sand and mud should not be laid down together. Some geologists attribute its formation to submarine avalanches or strong turbidity currents. These actions churn sediment and cause mixed-sediment slurries to occur. When this is the case, the rocks may exhibit a variety of sedimentary features. Supporting this theory is the fact that deposits of greywacke are found on the edges of the continental shelves, at the bottoms of oceanic trenches, and at the bases of mountain formational areas. It also occurs in association with black shales of deep sea origin. 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. ... Gravel Gravel is rock that is of a certain size range. ... Patterns in the sand Sand is an example of a class of materials called granular matter. ... In computer gaming, a MUD (multi-user dungeon, dimension, or sometimes domain) is a multi-player computer role-playing game typically running on a bulletin board system or Internet server. ... A geologist is a contributor to the science of geology. ... A Himalayan avalanche. ... The continental shelf is the extended perimeter of each continent, which is covered during interglacial periods such as the one we live in by relatively shallow seas and gulfs. ... Categories: Stub | Plate tectonics | Earth sciences | Landforms | Oceanic trenches ... Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ...

Greywackes are mostly grey, brown, yellow or black, dull-colored, sandy rocks which may occur in thick or thin beds along with slates and limestones. They are abundant in Wales, the south of Scotland, the Longford Massif in Ireland and the Lakes district of England. They can contain a very great variety of minerals, the principal ones being quartz, orthoclase and plagioclase feldspars, calcite, iron oxides and graphitic, carbonaceous matters, together with (in the coarser kinds) fragments of such rocks as felsite, chert, slate, gneiss, various schists, and quartzite. Among other minerals found in them are biotite and chlorite, tourmaline, epidote, apatite, garnet, hornblende and augite, sphene, pyrites. The cementing material may be siliceous or argillaceous, and is sometimes calcareous. Alternate meanings in Slate (disambiguation) Slate Slate is a fine-grained homogeneous sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). ... Media:Example. ... National motto: Cymru am byth (Welsh: Wales for ever) Waless location within the UK Official languages English and Welsh Capital Cardiff Largest city Cardiff First Minister Rhodri Morgan Area  - Total Ranked 3rd UK 20,779 km² Population  - Total (2001)  - Density Ranked 3rd UK 2,903,085 140/km² NUTS... Scotland (Alba in Scottish Gaelic) is a country or nation and former independent kingdom of northwest Europe, and one of the four constituent parts of the United Kingdom. ... Royal motto: Dieu et mon droit (French: God and my right) Englands location within the UK Official language English de facto Capital London de facto Largest city London Area  - Total Ranked 1st UK 130,395 km² Population  - Total (2001)  - Density Ranked 1st UK 49,138,831 377/km² Religion... Minerals are natural compounds formed through geological processes. ... 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. ... Calcite from Brushy Creek Mine, Missouri, USA. The mineral calcite is a carbonate of calcium corresponding to the formula CaCO3 and is one of the most widely distributed minerals on the Earths surface. ... 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. ... Felsite is a very fine to cryptocrystalline igneous rock that may or may not contain larger crystals, called phenocrysts, that are typical of many porphyritic igneous rocks. ... Chert Chert is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. ... Alternate meanings in Slate (disambiguation) Slate Slate is a fine-grained homogeneous sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). ... 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. ... Categories: Mineral stubs | Metamorphic rocks ... Quartzite Quartzite is a hard, metamorphic rock which was originally sandstone. ... A Biotite slice Biotite is a common silicate mineral that contains potassium, magnesium, iron and aluminium. ... Chlorite is a group of phyllosilicate minerals often classified as clays. ... The mineral tourmaline is chemically one of the most complicated silicate minerals. ... Epidote is a calcium aluminium iron sorosilicate mineral, Ca2(Al, Fe)3(SiO4)3(OH), crystallizing in the monoclinic system. ... 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. ... The Garnet group of minerals show crystals with a habit of dodecahedrons and trapezohedrons. ... Amphibole (Hornblende) The mineral hornblende is a complex silicate which is an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate. ... Augite Categories: Mineral stubs | Minerals | Silicate minerals ... Titanite or sphene is a calcium titanium nesosilicate mineral, CaTiSiO5. ... The mineral pyrite, or iron pyrite, is iron disulfide, FeS2. ...

As a rule greywackes are not fossiliferous, but organic remains may be common in the finer beds associated with them. Their component particles are usually not very rounded or polished, and the rocks have often been considerably indurated by recrystallization, such as the introduction of interstitial silica. In some districts the greywackes are cleaved, but they show phenomena of this kind much less perfectly than the slates. Some varieties include feldspathic greywacke, which is rich in feldspar, and lithic greywacke, which is rich in tiny rock fragments. FOSSIL is a standard for allowing serial communication for telecommunications programs under DOS. FOSSIL stands for Fido Opus Seadog Standard Interface Layer and was made by a group of Fidonet sysops to make their software work on different machines. ... Recrystallization is an essentially physical process that has meanings in chemistry and geology. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ...

Although the group is so diverse that it is difficult to characterize mineralogically, it has a well-established place in petrographical classifications because these peculiar composite arenaceous deposits are very frequent among Silurian and Cambrian rocks, and rarely occur in Secondary or Tertiary strata. Their essential features are their gritty character and their complex composition. By increasing metamorphism, greywackes frequently pass into mica-schists, chloritic schists and sedimentary gneisses. Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. ... Alternate use: The Silurians, a reptilian race from the science fiction series Doctor Who. The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 439 million years before the present (BP), to the beginning of the Devonian period, about 408. ... The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon_geology and ended about 490 million years BP with the beginning of the Ordovician period. ... Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. ...

External links

• Greywacke images (http://mysite.wanadoo-members.co.uk/geology_revision/greywacke.html)
• NPS site Presidio (http://www.nps.gov/prsf/geology/graywack.htm)
• Franciscan Greywacke/Shales (http://www.marin.cc.ca.us/~jim/ring/rgrey.html)

This article incorporates text from the public domain 1911 Encyclopædia Britannica. The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ... The Eleventh Edition of the Encyclopædia Britannica ( 1911) in many ways represents the sum of knowledge at the beginning of the 20th century. ...