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Glossary of Geological Terms

Agate: quartz mineral with characteristic banding, form of the Chalcedony; mostly in cavities of eruptive rocks (melaphyr-mandelstones; e.g. Idar-Oberstein).

Ammonites: extinct group of cephalopods with outer calcareous shell. The shell was usually curled into a spiral. Many ammonites are excellent guide fossils; they occured from the Lower Devon until the end of the Cretaceous era; there are more than 5000 species.

Amphiboles: rock-forming group of minerals; containing magnesium, iron, calcium, sodium, aluminum or titanium.

Andesite: medium to dark gray, often porphyritic eruptive rock with fine-grained, partly glassy groundmass with inclusions of plagioclase, biotite, hornblende or pyroxenes.

Aragonite: rock very similar to calcite (CaCO3); component of the shells and skeletons of many animals.

Arkose: sandstone with a high proportion of feldspars (over 25%) and mica; formed under dry-hot conditions by weathering of Rocks rich in such minerals (e.g., gneiss and granite).

Belemnites: extinct order of cephalopods from the Lower Carboniferous until the Upper Chalk. They had an elongated body with an internal skeleton. Mostly only the massive, pointed body end ("thunderbolts") has been preserved. Important guide fossils for the Jurasic und Cretaceous eras.

Biotite: dark green or brown to black mineral from the group of of the mica.

Breccia: coarse-grained sedimentary rock; consolidated debris composed of angular pieces of rock and minerals cemented by clayey, calcareous, or siliceous binders.

Bruchtektonik (Fracture tectonics): fracturing and dislocation phenomena of the earth's crust, associated with the formation of fractures, fissures, and faults.

Bunte Schiefer (Variegated slate): oldest Devonian strata in the Hunsrück; mainly composed of clay, but can also consist of coarse rubble.

Calcite (Kalkspat): mostly transparent, white mineral of the chemical composition CaCO3 (calcium carbonate); frequently occurring, often rock-forming.

Chalcedony: cryptocrystalline variety of quartz; multicolored or colorless, translucent.

Dacite: silica-rich eruptive rock with plagioclase inclusions, quartz, biotite, hornblende and others in dense, partly glassy groundmass.

Diorite: light, granular bedrock.

Dolomite: granular to dense layered rock, which consists mainly of magnesium carbonate and calcite; weathered in very characteristic form (e.g., Dolomites in South Tyrol).

Druse: cavity in rocks lined with crystals.

Einsprengling (Inclusion): larger single crystal in the groundmass of magmatic rocks.

Ergussgestein (Volcanic rock: Vulcanites): magmatic rocks, which are formed in the course of volcanic activity by solidification of the liquid magma from the earth's interior on the earth's surface.

Erosion: removal of the earth's surface, especially by the incising and clearing out activity of the flowing water.

Eruption: collective term for volcanic eruptive activity, in particular the outflow of liquid magma from the earth's interior to the earth's surface.

Faltung (Folding): upward and downward bending of rock strata caused by lateral pressure and constriction of rock layers.

Faulschlamm (Sapropel): black sludge at the bottom of nutrient-rich waters; very rich in fat and protein; precursor of petroleum formation.

Facies (Metamorphic facies): features that are characteristic of the formation of a sedimentary rock.

Feldspars: group of rock-forming silicates; subdivisible into alkali feldspars and plagioclases.

Fossils: remains of animals or plants (also their traces of life) from the geological past.

Gebirgsbildung (Orogenesis: Mountain building): deformation of limited areas of the earth's crust caused by uplift and subsidence processes; with rock displacements, folding, fracture tectonics, volcanism and earthquakes leading to surface forms with high relief energy. It is primarily caused by movements of the earth's mantle.

Geology: study of the origin, development and change of the earth and the living creatures inhabiting it in geological time.

Geosyncline: extensive subsidence area of the earth's crust in which large quantities of sedimentary rocks accumulate. These can later, after folding, be lifted out as mountains.

Gesteine (Rocks): natural, solid formations within the earth's crust; according to their formation, a distinction is made between igneous, sedimentary and metamorphic rocks.

Glimmer (Mica): flake-like silicates.

Gneiss: group of metamorphic rocks with quartz, feldspar and mica as main constituents; formed from igneous rocks (ortogneiss) or sedimentary rocks (paragneiss).

Granite: in terms of quantity, the most common deep rock with the main constituents of feldspar, quartz and mica; occurs in the form of thick massifs (boulders) as well as in veins.

Greenschist: weakly metamorphic, fine-grained rocks with a schistose structure; they are formed from clay-marly sedimentary rocks or basic igneous rocks.

Grus (Rock debris): fine rock debris formed by weathering.

Härtling (Hard rock): elevation outstanding above its surroundings due to its resistance to erosion and weathering.

Hornblende: important mineral from the group of amphiboles; main component of many rocks, e.g. of the hornblende slate.

Intrusion: process of penetration and solidification of magma in rocks of the earth's solid crust.

Kalkspat (Calcite): mostly transparent, white mineral of the chemical composition CaCO3 (calcium carbonate). composition CaCO3 (calcium carbonate); frequently occurring, often rock-forming.

Kalkstein (Limestone): sedimentary rock consisting predominantly of calcite, but also of aragonite or dolomite; forms by chemical precipitation or from lime shells and skeletons of animals or plant organisms.

Kies (Gravel): crushed, sedimentary unconsolidated rock; consists of rock fragments or ice rounded rock fragments.

Klastische Gesteine (Clastic rocks, debris rocks): sedimentary rocks that have been formed from the fragments of older rocks.

Konglomerat (Conglomerate): coarse-grained sedimentary rock consisting of rounded rock fragments (boulders), which are cemented by clayey, calcareous, siliceous or ferruginous binders.

Kontaktmetamorphose (Contact metamorphism): rock transformation that has been caused by contact with rising hot magma.

Korrosion (Corrosion): decomposition of rocks by the chemical action of water and the acids, bases and salts dissolved in it.

Lava: the hot magma escaping to the earth's surface from vents and fissures during volcanic eruptions; also a term for the resulting rock mass. The solidification forms depend on temperature, viscosity (flowability) and gas content of the molten rock.

Leitfossilien (Guide fossils): fossil animal and plant species ("fossils") that are characteristic of geological strata or strata sequences with the same geological age.

Liparite (Rhyolite): light gray, reddish or greenish eruptive rock with inclusions of plagioclase, quartz, biotite and others in an often glassy groundmass; geologically older rhyolite is called quartz-porphyry.

Magma: glowing, liquid, predominantly silicate (consisting of silicates) melt from the depths of the earth. One distinguishes between the processes of the volcanism at or directly under the earth's surface and the processes of plutonism, which take place at greater depths.

Magmatic rocks (Magmatites): the rocks formed by solidification of magma. A distinction is made between volcanic rocks (e.g. basalt), plutonites (e.g. Granite) and the intermediate gangue rocks.

Magmatite (Magmatic rocks): the rocks formed by solidification of magma. A distinction is made between volcanic rocks (e.g. basalt), plutonites (e.g. Granite) and the intermediate gangue rocks.

Melaphyre: igneous rock of basaltic composition; usually of dark or dark green color, often weathering reddish; melaphyre mandelstones yield agates (e.g., in Idar-Oberstein)).

Mergel (Marl): stratified rocks consisting mainly of clay and limestone (clay marl and lime marl).

Metamorphic rocks: the rocks formed by metamorphism; unlike "ortho-rocks" which originate from igneous rocks (e.g., granites), "para-rocks" are formed from sediments, e.g. quartzites, marbles, schists, gneisses.

Metamorphism: the transformation and reshaping of a rock by high pressure and temperature.

Minerals: the constituents of rocks that are uniform in terms of their physical and chemical properties.

Moraine: the rock material carried and deposited by glaciers.

Nepheline: feldspar representative; common in basalts.

Olivine: group of rock-forming minerals.

Orogenesis (Mountain building): deformation of limited areas of the earth's crust caused by uplift and subsidence processes; with rock displacements, folding, fracture tectonics, volcanism and earthquakes leading to surface forms with high relief energy. It is primarily caused by movements of the earth's mantle.

Paleontology: includes the branches of science that deal with the study of the ancient animal and plant world.

Phyllite: greenish-gray, silky shiny, fine-foliated shale; formed by metamorphosis from clay shales.

Plagioclase: rock-forming mineral from the feldspar group.

Plutonism: formation, alteration and migration of natural rock melts within the Earth's crust; the solidified rocks at greater depths are called deep rocks or "plutonites"; large deep rock bodies in the earth's crust are called "plutons".

Plutonite (Deep rocks): igneous rocks, which are formed by the solidification of magma in the deeper crust of the earth.

Porphyry: collective term for igneous rocks with individual larger crystals (mostly alkali feldspars and/or quartz) as inclusions in a fine-grained and dense groundmass. The term is used today only in compositions, e.g. quartz porphyry or granite porphyry.

Pyrite (Sulfur pyrite): common mineral in ore deposits.

Pyroxenes: group of rock-forming minerals; mostly green or brown to black; crystals mostly columnar to stalked.

Quartz: group of important rock-forming minerals; always present in crystallized form.

Quartzite: very hard, mostly dense, fine-grained, mainly of Quartz, metamorphic rock; it formed from sandstone (also called called rock quartzite).

Quartz porphyry: reddish colored eruptive rock; occurs in the Red-Lying era.

Rhyolith (Liparite): light gray, reddish or greenish eruptive rock with inclusions of plagioclase, quartz, biotite and others in an often glassy groundmass; geologically older rhyolite is called quartz-porphyry.

Sandstone: sedimentary rock consisting largely of quartz grains, cemented by a clayey, siliceous or ferruginous binder.

Sapropel (Faulschlamm): black sludge at the bottom of nutrient-rich waters; very rich in fat and protein; precursor of petroleum formation.

Schicht (Layer): a rock body of areal extent formed by deposition. Individual layers are separated from each other by bedding joints.

Schiefer (Slate): a rock formed by tectonic processes and metamorphism; in thin, flat plates breaking rock.

Sedimentation: process of separating or settling solid substances that are transported by water.

Sedimentary rock (Layered rock): a rock formed by the consolidation of sediments; clastic sediments consist of mechanically crushed rock fragments of various grain sizes; chemical sediments are formed by precipitation of dissolved constituents from fluids; biogenic sediments form under substantial participation of animal or vegetable organisms.

Silicates: the most important rock-forming minerals of the earth (silicon); they include quartz, feldspar and mica.

Störung (Discontinuity): separation joint where an adjustment of two rock layers has taken place.

Syncline: depression in a geological fold.

Taunus quartzite: relief-determining quartzite in Hunsrück with high quartz content; difficult to weather.

Tectonics: branch of geology that deals with the structure of the earth's crust and the movements and forces that affect the earth's crust.

Tiefengesteine (Plutonite): igneous rocks, which are formed by the solidification of magma in the deeper crust of the earth.

Tone (Clays): fine-grained, clastic unconsolidated rocks that consist mainly of clay minerals, which are newly formed during weathering.

Tonschiefer (Clay schist): thin-slate clay rock that splits into flat plates along parallel cleavage planes; formed by tectonic pressure and slight metamorphosis from slate clay (e.g. roofing slate).

Trümmergesteine (Debris rocks, clastic rocks): sedimentary rocks that have been formed from the fragments of older rocks.

Tuff: solidified volcanic ash.

Verwerfung (Discontinuity): the relative displacement of two rock layers along the length of a fault.

Verwitterung (Weathering): the decay of rocks and minerals at or near the earth's surface caused by the action of physical-mechanical, chemical, and biological influences. Type and intensity of weathering depend on rock and climate. Weathering is a prerequisite for the formation of sedimentary rocks and the formation of soil.

Volcanism: all geological processes associated with the escape of solid, liquid or gaseous substances from the earth's interior to the surface. Volcanic activity occurs mainly in tectonic zones of weakness (e.g., faults), or at stable melting zones in the Earth's mantle ("hot spots").

Volcanic rocks (Eruptive rocks): igneous rocks formed during volcanic activity by solidification of the liquid magma at the earth's surface.

 

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