Bentorite is a

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.John P. Rafferty, ed. (2 ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

Ca₆(Cr,Al)₂(SO₄)₃(OH)₁₂·26H₂O. It is colored violet to light violet. Its crystals are

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

to dihexagonal dipyramidal. It is transparent and has vitreous luster. It has perfect cleavage. It is not

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

. Bentorite is rated 2 on the Mohs Scale. The mineral was first described in 1980 by

Shulamit Gross Shulamit Gross (Hebrew: שולמית גרוס; lived 1 October 1923 – 19 Sep 2012) was an Israeli mineralogist and geologist who studied the Hatrurim Formation. Biography Gross was born as Shulamit Lifszyc in Grodno, Poland (today, Hrodna, B ...

for an occurrence in the

Hatrurim Formation The Hatrurim Formation or ''Mottled Zone'' is a geologic formation with outcrops all around the Dead Sea Basin: in the Negev Desert in Israel, in the Judaean Desert on the West Bank, and in western Jordan. It includes late Cretaceous to Eocene age ...

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretace ...

age along the western margin of the Dead Sea,

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

. It was named by its discoverer, Shulamit Gross, for

Yaakov Ben-Tor Yaakov Ben-Tor ( he, יעקב בן-תור; 1910–2002) was an Israeli geologist. Biography Ben-Tor was born as Kurt Winter in the Baltic city of Königsberg, East Prussia, Germany, (since 1945 Kaliningrad, now in Russia) in 1910. Winter began ...

(1910–2002), Professor at the Hebrew University of Jerusalem and the

University of California, San Diego The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is t ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

, US, for his contributions to geology and mineralogy in Israel.Handbook of Mineralogy
/ref>- Webmineral data
/ref>

Formation

The only naturally occurring bentorite that has been discovered is in the Hatrurim Formation near the Dead Sea in Israel. The formation consists of a mixture of

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s, and marls. The original sediments were enriched in chromium, and later experienced heating to >1000 °C at atmospheric pressure. This formed a natural

Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th ...

which has since been hydrated from

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

and/or

rainwater Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water fo ...

to form a natural

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...

. The source of the heat is thought to be due to

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

, or

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

. Following this combustion metamorphosis, highly alkaline fluids penetrated and altered the rock to form supergene veins of bentorite.

Applications

When suitably prepared,

contains crystals of

ettringite Ettringite is a hydrous calcium aluminium sulfate mineral with formula: . It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of ...

that can exchange aluminium for chromium, converting the ettringite to bentorite. This allows concretes to sequester chromium present as an environmental pollutant.

References

Calcium minerals Chromium minerals Aluminium minerals Sulfate minerals Hexagonal minerals Minerals in space group 194 {{sulfate-mineral-stub

Formation

Applications

See also

References