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Riebeckite is a -rich member of the group of , chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a series with magnesioriebeckite. It crystallizes in the system, usually as long prismatic showing a diamond-shaped cross section, but also in fibrous, bladed, acicular, columnar, and radiating forms. Its is 5.0–6.0, and its is 3.0–3.4. Cleavage is perfect, two directions in the shape of a ; fracture is uneven, splintery. It is often translucent to nearly opaque.

Name and discovery
Riebeckite was first described in 1888 for an occurrence on , Aden Governorate, , and named for German explorer (1853–1885).

The mineral is also known as crocidolite.

(2006). 9780309101691, National Academies Press. .

Riebeckite typically forms dark-blue elongated to fibrous crystals in highly alkali , , rarely in , granite and . It occurs in banded iron formations as the variety crocidolite (blue ). It occurs in association with , , , in ; with , ferro- in ; and with , , , , , , , in iron formations.

Riebeckite granite
The riebeckite known as ailsite, found on the island of in western , is prized for its use in the manufacture of stones.

Riebeckite granite was used for the facing stones of the from Moyles Quarry (a.k.a. Canton Viaduct Quarry) now part of Borderland State Park in , US. The commonwealth's name is even taken from an Algonquian word for the Great Blue Hill, which got its color from this form of granite.

Crocidolite (fibrous riebeckite)
The fibrous forms of riebeckite are known as crocidolite and are one of the six recognised types of . Often referred to as blue asbestos, it is considered the most hazardous. The association between blue asbestos and was established by J. C. Wager, C. A. Sleggs, and P. Marchand by 1960.

Crocidolite asbestos was mined in , , and Wittenoom, Western Australia. Bolivian crocidolite was used in approximately 13 billion Kent Micronite cigarette filters, manufactured from March 1952 until at least May 1956 by the Lorillard Tobacco Company (now part of the R. J. Reynolds Tobacco Company). Blue asbestos was also used to similar effect, and hazard, in early gas masks.

See also

External links
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