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Aragonite

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Aragonite crystal structure
Aragonite crystal structure

Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO3 (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including precipitation from marine and freshwater environments.

Aragonite Crystal Structure
Aragonite Crystal Structure

The crystal lattice of aragonite differs from that of calcite, resulting in a different crystal shape, an orthorhombic crystal system with acicular crystal.[1] Repeated twinning results in pseudo-hexagonal forms. Aragonite may be columnar or fibrous, occasionally in branching helictitic forms called flos-ferri ("flowers of iron") from their association with the ores at the Carinthian iron mines.[2]

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Carbonate mineral

Carbonate mineral

Carbonate minerals are those minerals containing the carbonate ion, CO2−3.

Calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of eggshells, gastropod shells, shellfish skeletons and pearls. Things containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

Calcium

Calcium

Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust, and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Carbonate

Carbonate

A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−3. The word carbonate may also refer to a carbonate ester, an organic compound containing the carbonate group C(=O)(O–)2.

Mineral

Mineral

In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.

Calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses.

Orthorhombic crystal system

Orthorhombic crystal system

In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height (c), such that a, b, and c are distinct. All three bases intersect at 90° angles, so the three lattice vectors remain mutually orthogonal.

Acicular (crystal habit)

Acicular (crystal habit)

Acicular, in mineralogy, refers to a crystal habit composed of slender, needle-like crystals. Crystals with this habit tend to be fragile. Complete, undamaged acicular specimens are uncommon.

Crystal twinning

Crystal twinning

Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly bonded to each other. The surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane.

Helictite

Helictite

A helictite is a speleothem found in a limestone cave that changes its axis from the vertical at one or more stages during its growth. Helictites have a curving or angular form that looks as if they were grown in zero gravity. They are most likely the result of capillary forces acting on tiny water droplets, a force often strong enough at this scale to defy gravity.

Ore

Ore

Ore is natural rock or sediment that contains one or more valuable minerals concentrated above background levels, typically containing metals, that can be mined, treated and sold at a profit. The grade of ore refers to the concentration of the desired material it contains. The value of the metals or minerals a rock contains must be weighed against the cost of extraction to determine whether it is of sufficiently high grade to be worth mining, and is therefore considered an ore. A complex ore is one containing more than one valuable mineral.

Duchy of Carinthia

Duchy of Carinthia

The Duchy of Carinthia was a duchy located in southern Austria and parts of northern Slovenia. It was separated from the Duchy of Bavaria in 976, and was the first newly created Imperial State after the original German stem duchies.

Occurrence

The type location for aragonite is Molina de Aragón in the Province of Guadalajara in Castilla-La Mancha, Spain, for which it was named in 1797.[3] Aragonite is found in this locality as cyclic twins inside gypsum and marls of the Keuper facies of the Triassic.[4] This type of aragonite deposit is very common in Spain, and there are also some in France.[2]

An aragonite cave, the Ochtinská Aragonite Cave, is situated in Slovakia.[5]

In the US, aragonite in the form of stalactites and "cave flowers" (anthodite) is known from Carlsbad Caverns and other caves.[6] For a few years in the early 1900s, aragonite was mined at Aragonite, Utah (now a ghost town).[7]

Massive deposits of oolitic aragonite sand are found on the seabed in the Bahamas.[8]

Aragonite is the high pressure polymorph of calcium carbonate. As such, it occurs in high pressure metamorphic rocks such as those formed at subduction zones.[9]

Aragonite forms naturally in almost all mollusk shells, and as the calcareous endoskeleton of warm- and cold-water corals (Scleractinia). Several serpulids have aragonitic tubes.[10] Because the mineral deposition in mollusk shells is strongly biologically controlled,[11] some crystal forms are distinctively different from those of inorganic aragonite.[12] In some mollusks, the entire shell is aragonite;[13] in others, aragonite forms only discrete parts of a bimineralic shell (aragonite plus calcite).[11] The nacreous layer of the aragonite fossil shells of some extinct ammonites forms an iridescent material called ammolite.[14]

Aragonite also forms naturally in the endocarp of Celtis occidentalis.[15]

Aragonite also forms in the ocean inorganic precipitates called marine cements (in the sediment) or as free crystals (in the water column).[16][17] Inorganic precipitation of aragonite in caves can occur in the form of speleothems.[18] Aragonite is common in serpentinites where magnesium-rich pore solutions apparently inhibit calcite growth and promote aragonite precipitation.[19]

Aragonite is metastable at the low pressures near the Earth's surface and is thus commonly replaced by calcite in fossils. Aragonite older than the Carboniferous is essentially unknown.[20] It can also be synthesized by adding a calcium chloride solution to a sodium carbonate solution at temperatures above 60 °C (140 °F) or in water-ethanol mixtures at ambient temperatures.[21]

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Molina de Aragón

Molina de Aragón

Molina de Aragón is a municipality located in the province of Guadalajara, Castile-La Mancha, Spain. According to the 2009 census (INE), the municipality had a population of 3,671 inhabitants. It holds the record (−28.2 °C) for the lowest temperature measured by a meteorological station in Spain.

Province of Guadalajara

Province of Guadalajara

Guadalajara is a province of Spain, belonging to the autonomous community of Castilla–La Mancha. As of 2019 it had a population of 258,890 people. The population of the province has grown in the last 10 years. It is located in the centre of the Iberian Peninsula.

Spain

Spain

Spain, or the Kingdom of Spain, is a country primarily located in southwestern Europe with parts of territory in the Atlantic Ocean and across the Mediterranean Sea. The largest part of Spain is situated on the Iberian Peninsula; its territory also includes the Canary Islands in the Atlantic Ocean, the Balearic Islands in the Mediterranean Sea, and the autonomous cities of Ceuta and Melilla in Africa. The country's mainland is bordered to the south by Gibraltar; to the south and east by the Mediterranean Sea; to the north by France, Andorra and the Bay of Biscay; and to the west by Portugal and the Atlantic Ocean. With an area of 505,990 km2 (195,360 sq mi), Spain is the second-largest country in the European Union (EU) and, with a population exceeding 47.4 million, the fourth-most populous EU member state. Spain's capital and largest city is Madrid; other major urban areas include Barcelona, Valencia, Seville, Zaragoza, Málaga, Murcia, Palma de Mallorca, Las Palmas de Gran Canaria, and Bilbao.

Gypsum

Gypsum

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. Alabaster, a fine-grained white or lightly tinted variety of gypsum, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire, and the Nottingham alabasters of Medieval England. Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite.

Keuper

Keuper

The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolomite, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs. The Keuper lies on top of the Muschelkalk and under the predominantly Lower Jurassic Lias or other Early Jurassic strata.

Ochtinská Aragonite Cave

Ochtinská Aragonite Cave

Ochtinská Aragonite Cave is a unique aragonite cave situated in southern Slovakia, near Rožňava. Although only 300 m long, it is famous for its rare aragonite formations.

Slovakia

Slovakia

Slovakia, officially the Slovak Republic, is a landlocked country in Central Europe. It is bordered by Poland to the north, Ukraine to the east, Hungary to the south, Austria to the southwest, and the Czech Republic to the northwest. Slovakia's mostly mountainous territory spans about 49,000 square kilometres (19,000 sq mi), with a population of over 5.4 million. The capital and largest city is Bratislava, while the second largest city is Košice.

Stalactite

Stalactite

A stalactite (, ; from the Greek 'stalaktos' via stalassein is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of lava, minerals, mud, peat, pitch, sand, sinter, and amberat. A stalactite is not necessarily a speleothem, though speleothems are the most common form of stalactite because of the abundance of limestone caves.

Anthodite

Anthodite

Anthodites (Greek ἄνθος ánthos, "flower", -ode, adjectival combining form, -ite adjectival suffix) are speleothems (cave formations) composed of long needle-like crystals situated in clusters which radiate outward from a common base. The "needles" may be quill-like or feathery. Most anthodites are made of the mineral aragonite (a variety of calcium carbonate, CaCO3), although some are composed of gypsum (CaSO4·2H2O).

Oolitic aragonite sand

Oolitic aragonite sand

Oolitic aragonite sand is composed of the calcium carbonate mineral, aragonite, with an egg-like shape and sand grain size. This sand type forms in tropical waters through precipitation, sedimentation, and microbial activity, and is indicative of high energy environments. The production of oolitic aragonite sand in the Bahamas surpasses anyplace else in the world. Changes in seawater chemistry and paleoenvironments can be interpreted by the sand's chemical composition and structure.

Polymorphism (materials science)

Polymorphism (materials science)

In materials science, polymorphism describes the existence of a solid material in more than one form or crystal structure. Polymorphism is a form of isomerism. Any crystalline material can exhibit the phenomenon. Allotropy refers to polymorphism for chemical elements. Polymorphism is of practical relevance to pharmaceuticals, agrochemicals, pigments, dyestuffs, foods, and explosives. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure to another phase of the same chemical composition with a different crystal structure." According to McCrone, polymorphs are "different in crystal structure but identical in the liquid or vapor states." Materials with two polymorphs are called dimorphic, with three polymorphs, trimorphic, etc.

Calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of eggshells, gastropod shells, shellfish skeletons and pearls. Things containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

Physical properties

Aragonite is not the thermodynamically stable phase of calcium carbonate at any pressure below about 3,000 bars (300,000 kPa) at any temperature.[22] Aragonite nonetheless frequently forms in near-surface environments at ambient temperatures. The weak van der Waals interactions inside aragonite give an important contribution to both the crystallographic and elastic properties of this mineral.[23] The difference in stability between aragonite and calcite, as measured by the Gibbs free energy of formation, is small, and effects of grain size and impurities can be important. The formation of aragonite at temperatures and pressures where calcite should be the stable polymorph may be an example of Ostwald's step rule, where a less stable phase is the first to form.[24] The presence of magnesium ions may inhibit calcite formation in favor of aragonite.[25] Once formed, aragonite tends to alter to calcite on scales of 107 to 108 years.[26] Comparing to the calcite, aragonite

The mineral vaterite, also known as μ-CaCO3, is another phase of calcium carbonate that is metastable at ambient conditions typical of Earth's surface, and decomposes even more readily than aragonite.[27][28]

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Thermodynamics

Thermodynamics

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.

Magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals it occurs naturally only in combination with other elements and it almost always has an oxidation state of +2. It reacts readily with air to form a thin passivation coating of magnesium oxide that inhibits further corrosion of the metal. The free metal burns with a brilliant-white light. The metal is obtained mainly by electrolysis of magnesium salts obtained from brine. It is less dense than aluminium and is used primarily as a component in strong and lightweight alloys that contain aluminium.

Calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses.

Vaterite

Vaterite

Vaterite is a mineral, a polymorph of calcium carbonate (CaCO3). It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3). Vaterite belongs to the hexagonal crystal system, whereas calcite is trigonal and aragonite is orthorhombic.

Uses

In aquaria, aragonite is considered essential for the replication of reef conditions. Aragonite provides the materials necessary for much sea life and also keeps the pH of the water close to its natural level, to prevent the dissolution of biogenic calcium carbonate.[29]

Aragonite has been successfully tested for the removal of pollutants like zinc, cobalt and lead from contaminated wastewaters.[30]

Claims that magnetic water treatment can reduce scaling, by converting calcite to aragonite, have been met with skepticism,[31] but continue to be investigated.[32][33]

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Aquarium

Aquarium

An aquarium is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquatic reptiles, such as turtles, and aquatic plants. The term aquarium, coined by English naturalist Philip Henry Gosse, combines the Latin root aqua, meaning 'water', with the suffix -arium, meaning 'a place for relating to'.

Calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of eggshells, gastropod shells, shellfish skeletons and pearls. Things containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

Zinc

Zinc

Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic table. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).

Cobalt

Cobalt

Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver metal.

Lead

Lead

Lead is a chemical element with the symbol Pb and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is a shiny gray with a hint of blue. It tarnishes to a dull gray color when exposed to air. Lead has the highest atomic number of any stable element and three of its isotopes are endpoints of major nuclear decay chains of heavier elements. Lead is toxic, even in small amounts, especially to children.

Magnetic water treatment

Magnetic water treatment

Magnetic water treatment is a method of supposedly reducing the effects of hard water by passing it through a magnetic field as a non-chemical alternative to water softening. Magnetic water treatment is regarded as unproven and unscientific. A 1996 study by Lawrence Livermore National Laboratory found no significant effect of magnetic water treatment on the formation of scale.

Fouling

Fouling

Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms (biofouling) or a non-living substance. Fouling is usually distinguished from other surface-growth phenomena in that it occurs on a surface of a component, system, or plant performing a defined and useful function and that the fouling process impedes or interferes with this function.

Gallery

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Baculites

Baculites

Baculites is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph ammonites. The genus, which lived worldwide throughout most of the Late Cretaceous, and which briefly survived the K-Pg mass extinction event, was named by Lamarck in 1799.

Pierre Shale

Pierre Shale

The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from Pembina Valley in Canada to New Mexico.

Cretaceous

Cretaceous

The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

Scanning electron microscope

Scanning electron microscope

A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector. The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. Some SEMs can achieve resolutions better than 1 nanometer.

Nacre

Nacre

Nacre, also known as mother of pearl, is an organic–inorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent.

Blue mussel

Blue mussel

The blue mussel, also known as the common mussel, is a medium-sized edible marine bivalve mollusc in the family Mytilidae, the mussels. Blue mussels are subject to commercial use and intensive aquaculture. A species with a large range, empty shells are commonly found on beaches around the world.

Source: "Aragonite", Wikipedia, Wikimedia Foundation, (2023, March 5th), https://en.wikipedia.org/wiki/Aragonite.

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References
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