Cummingtonite ( ) is a metamorphic

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...

with the

chemical composition A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...

, magnesium iron silicate hydroxide. Monoclinic cummingtonite is compositionally similar and polymorphic with orthorhombic

anthophyllite Anthophyllite is an orthorhombic amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of antho ...

, which is a much more common form of

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 (group 2 of the periodic ta ...

-rich amphibole, the latter being

metastable In chemistry and physics, metastability denotes an intermediate Energy level, energetic state within a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slope is a simple example of me ...

. Cummingtonite shares few compositional similarities with

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

amphiboles such as

arfvedsonite Arfvedsonite () is a sodium amphibole mineral with composition: aNa2] Fe2+)4Fe3+(OH)2, Si8O22]. It crystallizes in the monoclinic prismatic crystal system and typically occurs as greenish black to bluish grey fibrous to radiating or stellate pr ...

glaucophane Glaucophane is the name of a mineral and a mineral group belonging to the sodic amphibole supergroup of the double chain inosilicates, with the chemical formula ☐Na2(Mg3Al2)Si8O22(OH)2. Glaucophane crystallizes in the monoclinic system. Name G ...

riebeckite Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long prisma ...

. There is little solubility between these minerals due to different

crystal habit In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. The habit of a crystal is dependent on its crystallographic form and growth conditions, which generally creates irregularities due to l ...

and inability of substitution between alkali elements and ferro-magnesian elements within the amphibole structure.

Name and discovery

Cummingtonite - Dannemora Mine, Uppsala Län, Uppland, Sweden

Cummingtonite was named after the town of

Cummington, Massachusetts Cummington is a town in Hampshire County, Massachusetts, United States. The population was 829 at the 2020 census, down from 872 at the 2010 census. It is part of the Springfield, Massachusetts Metropolitan Statistical Area. History Cummington ...

, where it was discovered in 1824.

Chester Dewey Chester Dewey (October 25, 1784 – December 15, 1867) was an American botanist, antislavery activist, clergyman and educator.Makers of American Botany, Harry Baker Humphrey, Ronald Press Company, Library of Congress Card Number 61-18435 Early li ...

, "A Sketch of the Geology and Mineralogy of the Western Part of Massachusetts, and a Small Part of Adjoining States", in ''American Journal of Science'', first series, vol. 8, part 2, 1824, p. 1-60 It is also found in

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

, and

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

Chemistry

Cummingtonite is a member of the cummingtonite-

grunerite Grunerite is a mineral of the amphibole group of minerals with formula Fe7 Si8 O22( OH)2. It is the iron endmember of the grunerite-cummingtonite series. It forms as fibrous, columnar or massive aggregates of crystals. The crystals are monoclini ...

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word ...

series which ranges from for

magnesiocummingtonite Magnesiocummingtonite is the magnesium rich endmember of the cummingtonite-grunerite series of the amphibole group of minerals, with the following composition: (Mg)7Si8O22(OH)2. Magnesiocummingtonite is considered to be an aptly named magnesium r ...

to the iron rich grunerite endmember . Cummingtonite is used to describe minerals of this formula with between 30 and 70 per cent . Thus, cummingtonite is the series intermediate.

Manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

also substitutes for ) within cummingtonite amphibole, replacing B site atoms. These minerals are found in high-grade metamorphic

banded iron formation Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness a ...

and form a compositional series between (tirodite) and (dannemorite).

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 ...

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

and

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

concentrations in cummingtonite are low. Cummingtonite tends toward more

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 ...

substitution than related

. Similarly, cummingtonite has lower

ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to spe ...

iron and

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

than anthophyllite. Amosite is a rare

asbestiform Asbestiform is a crystal habit. It describes a mineral that grows in a fibrous aggregate of high tensile strength, flexible, long, and thin crystals that readily separate.Committee on Asbestos: Selected Health Effects, 2006, ''Asbestos: Selected Can ...

variety of grunerite that was mined as asbestos only in the eastern part of the

Transvaal Province The Province of the Transvaal ( af, Provinsie van Transvaal), commonly referred to as the Transvaal (; ), was a province of South Africa from 1910 until 1994, when a new constitution subdivided it following the end of apartheid. The name "Trans ...

. The origin of the name is ''Amosa'', the acronym for the mining company "Asbestos Mines of South Africa".

Occurrence

Cummingtonite is commonly found in metamorphosed magnesium-rich rocks and occurs in amphibolites. Usually it coexists with

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...

actinolite Actinolite is an amphibole silicate mineral with the chemical formula . Etymology The name ''actinolite'' is derived from the Greek word ''aktis'' (), meaning "beam" or "ray", because of the mineral's fibrous nature. Mineralogy Actinolite is ...

, magnesium clinochlore

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous ac ...

talc Talc, or talcum, is a Clay minerals, clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thi ...

, serpentine-

antigorite Antigorite is a lamellated, monoclinic mineral in the phylosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe2+)3Si2O5(OH)4. It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentinite ...

minerals or metamorphic

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

. Magnesium-rich cummingtonite can also coexist with

. Cummingtonite has also been found in some

felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...

volcanic rocks Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geology), rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of Volcano, volcanic origin. Like all rock types, ...

such as

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

rich species can be found in metamorphosed Mn-rich rock units. The

end member is characteristic of the metamorphosed iron formations of the

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...

region and the

Labrador Trough The Labrador Trough or the New Quebec Orogen is a long and wide geologic belt in Canada, extending south-southeast from Ungava Bay through Quebec and Labrador. The trough is a linear belt of sedimentary and volcanic rocks which developed in an ...

. With prograde metamorphism cummingtonite and grunerite morph to members of the

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

and pyroxene series.

Name and discovery

Chemistry

Occurrence

References

Further reading