#sedimentary rock

• Aquitanian — The first geochronological stage or subdivision of the early Miocene epoch, situated at the base of the Neogene period, covering a time interval from around twenty million years ago; also, as an adjective, it describes geological elements from this stage or refers to the Aquitaine region in France and its historical inhabitants. This structural term marks a major transitional geological period, defined by global climatic shifts and significant tectonic movements.
• Aleurite — A friable, unconsolidated, or weakly consolidated sediment composed of fine mineral fragments (chiefly quartz, feldspars, and clay minerals) whose dimensions are intermediate between those of sand and clay (ranging from 0.002 to 0.06 millimeters). It represents the main component of dust and loess, transforming through diagenesis and geological compaction into the sedimentary rock known as aleurite or siltstone.
• Aleurolite — A consolidated detrital sedimentary rock formed through the cementation and diagenesis of aleurite (fine mineral dust, chiefly quartzous). The dimensions of its component grains are intermediate between those of sandstones and argillites, ranging from 0.002 to 0.06 millimeters. It often exhibits fine stratification and is used in geology to reconstruct ancient fossil or lacustrine sedimentary environments.
• Allogenous — Of a different origin, born or formed elsewhere than its current location; an element (mineral, rock fragment, population, or individual) that is foreign to the indigenous environment in which it is integrated. In geology, it defines minerals transported from the outside and deposited in a sedimentary basin, while in sociology and anthropology, it refers to population groups originating from a geographic or cultural region different from the native one.
• Ammonite — A fossil marine cephalopod mollusk from the Ammonoidea subclass, characterized by an external, planospiral, and chambered calcareous shell, which lived from the Devonian period until the end of the Cretaceous. The fossils of these organisms are widely used in stratigraphical geology as index fossils for the precise dating of sedimentary rock layers from the Mesozoic era.
• Anisian — A geological stage or substage located at the base of the Middle Triassic epoch, chronologically spanning from approximately 247 to 242 million years ago. As an adjective, the term refers to rocks, sediments, or fossils formed during this time interval, internationally defined by the appearance of specific ammonite and conodont assemblages within reference Alpine geological sections.
• Anthracolitic — Belonging to, referring to, or specific to anthracolite or the geological period of formation of massive superior coal deposits combined with calcareous structures; a sedimentary rock or crystalline formation characterized by intercalations of calcium carbonate and organic fossil inclusions rich in fixed carbon. In a stratigraphic sense, it describes structural elements or petrographic layers that preserve physical and chemical properties from the Paleozoic era.
• Antras — An archaic or regional technical term used to describe an inferior variety of friable bituminous coal or fine coal dust sedimented in old extraction galleries, featuring a high content of mineral impurities and ash. In petrography, it can refer to microscopic fragments of carbonized organic matter dispersed in argillaceous sedimentary rocks, used as indicators of thermal metamorphism grade.
• Arkose — A coarse-grained detrital sedimentary rock, similar to sandstone, structurally formed by the disintegration of granite or other plutonic rocks and composed of a high percentage of feldspar (over 25%) alongside quartz and mica. Geologically, the presence of arkose in a terrestrial stratum indicates rapid mechanical weathering and short-distance transport in an arid or semi-arid climate, where chemical alteration was minimized.
• Arenaceous — Having the nature, appearance, or composition of sand; rich in sand grains or structurally formed from fine detrital quartz deposits. In a geological and mineralogical sense, it describes sedimentary rocks (such as sandstones or fine conglomerates) or soils whose primary textural matrix features a sandy granulometry according to lithological classification standards.
• Arenarie — An extremely rare term or obsolete variant previously used in sedimentology to designate a consolidated detrital sedimentary rock formed from cemented sand grains, currently known as sandstone. Its structural meaning stems from the Latin root relating to sand, indicating the coarse granulometric composition of the rock.
• Areniferous — Containing or producing sand; a rock, geological stratum, or detrital sedimentary deposit rich in silica grains or fine quartz. In a structural sense, it describes a lithological formation or terrestrial matrix built through massive clastic and sedimentary accumulations over geological eras, directly influencing the porosity and permeability of underlying aquifer layers.
• Arenogenic — Generating, producing, or favoring the formation of sand or sandy detrital deposits; relating to geological or morphological processes that lead to the fragmentation of siliceous rocks and the accumulation of quartz grains. In a structural-geological sense, an arenogenic factor directly determines the sedimentary dynamics of continental or coastal basins, influencing the granulometry of forming clastic layers.
• Argil — An archaic, etymological, or rare masculine variant for clay; a term used in ancient treatises on geology, mining, or crafting recipes from past centuries to describe the soft, sticky sedimentary rock. In an early industrial sense, it represented the clayey earth utilized as a binder or raw material in pottery and construction.
• Clay — An unconsolidated sedimentary rock with an extremely fine grain size (particles below 0.002 mm), primarily composed of hydrated aluminum silicates (clay minerals such as kaolinite, montmorillonite, or illite). It exhibits high plasticity when mixed with water, the property of hardening upon drying or firing at high temperatures, and is widely used in the ceramic industry, construction materials (bricks, cement), cosmetics, and medicine.
• Argilliferous — Containing clay, yielding, or sheltering massive deposits of clay; specific to sedimentary rocks or geological strata rich in clay minerals. In a scientific and structural sense, the adjective defines the quality of soils or detrital formations (such as argilliferous sandstones or argilliferous limestones) exhibiting high plasticity and impermeability properties due to the pelitic mineral fraction within their composition.
• Argillite — A compact argillaceous sedimentary rock, structurally formed through the diagenesis and deep cementation of clay muds, characterized by a higher hardness than simple clay and by the absence of fissility or the ability to split into thin sheets (unlike clay shales). In a geological sense, argillite represents an intermediate stage of metamorphism between soft pelitic sedimentary rocks and crystalline clay shales.
• Argillolite — A consolidated argillaceous sedimentary rock, structurally formed through the cementation, compaction, and deep dehydration of fine pelitic deposits (clay muds); a fine argillaceous sandstone or mudstone rock. In a geological sense, argilolitul is characterized by a massive texture, compact mass, and the absence of obvious fissility, representing a stable lithostratigraphic unit used in sedimentary basin analysis.