Crocidolite, variety of Riebeckite - Locality: Pomfret Mine, Vryburg, South Africa
Category Silicate mineral
Chemical formula [][Na2][(Fe2+)3(Fe3+)2][(OH)2|Si8O22]
Crystal symmetry Monoclinic 2/m
Unit cell a = 9.76 Å, b = 18.04 Å, c = 5.33 Å; β = 103.59°; Z=2
Color Black, dark blue; dark blue to yellow-green in thin section
Crystal habit As prismatic crystals, commonly fibrous, asbestiform; earthy, massive
Crystal system Monoclinic - Prismatic
Twinning Simple or multiple twinning parallel to {100}
Cleavage Perfect on {110}, intersecting at 56° and 124°; partings on {100} and {010}
Fracture Conchoidal to uneven
Tenacity Brittle
Mohs scale hardness 6
Luster Vitreous to silky
Streak Pale to bluish gray
Diaphaneity Semitransparent
Specific gravity 3.28 - 3.44
Optical properties Biaxial (-)
Refractive index nα = 1.680 - 1.698 nβ = 1.683 - 1.700 nγ = 1.685 - 1.706
Birefringence δ = 0.005 - 0.008
Pleochroism X = blue, indigo; Y = yellowish green, yellow brown; Z = dark blue
2V angle Measured: 68° to 85°, Calculated: 62° to 78°
Dispersion Strong
References [1][2][3]

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


Name and discovery

It was first described in 1888 for an occurrence on Socotra Island, Adan Governorate, Yemen and named for German explorer Emil Riebeck (1853-1885).[2]


It typically forms dark-blue elongated to fibrous crystals in highly alkali granites, syenites, rarely in felsic volcanics, granite pegmatites and schist. It occurs in banded iron formations as the asbestiform variety crocidolite ((crow-SEE-doe-lite) blue asbestos). It occurs in association with aegirine, nepheline, albite, arfvedsonite in igneous rocks; with tremolite, ferro-actinolite in metamorphic rocks; and with grunerite, magnetite, hematite, stilpnomelane, ankerite, siderite, calcite, chalcedonic quartz in iron formations.[1]

Riebeckite granite

Canton viaduct


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

Riebeckite granite was used for the facing stones of the Canton Viaduct from Moyles Quarry (a.k.a. Canton Viaduct Quarry) now part of Borderland State Park in Massachusetts, USA.

See also


External links

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Look at other dictionaries:

  • Riébeckite — Riébeckite[1] Catégorie IX : silicates[2] …   Wikipédia en Français

  • Riebeckite — La riebeckite est un minéral appartenant à la famille des amphiboles sodiques, de formule Na2(Fe,Mg)5Si8O22(OH)2. Description Elle cristallise dans le système monoclinique, généralement sous forme de longs cristaux prismatiques présentant une… …   Wikipédia en Français

  • RIEBECKITE — Faisant partie du groupe des amphiboles sodiques et monocliniques, la riebeckite est, comme l’ensemble de ce groupe, un inosilicate, c’est à dire que les tétraèdres silice oxygène sont disposés en rubans, doubles dans le cas présent. La formule… …   Encyclopédie Universelle

  • riebeckite — /ree be kuyt /, n. an amphibolic mineral, silicate of sodium and iron, occurring usually in feldspathoid rocks. [1885 90; named after Emil Riebeck (d. 1885), German explorer; see ITE1] * * * ▪ mineral       a sodium iron silicate mineral… …   Universalium

  • riebeckite — ribekitas statusas T sritis chemija apibrėžtis Mineralas. formulė Na₂Fe₃(II)Fe₂(III)[(OH,F)|Si₄O₁₁]₂ atitikmenys: angl. riebeckite rus. рибекит …   Chemijos terminų aiškinamasis žodynas

  • riebeckite — noun A form of amphibole rich in sodium …   Wiktionary

  • riebeckite — rie·beck·ite …   English syllables

  • riebeckite — ˈrēˌbeˌkīt noun ( s) Etymology: German riebeckit, from Emil Riebeck died 1885 German explorer + German it ite : a black monoclinic amphibole Na2Fe5Si8O22(OH)2 containing much iron and sodium …   Useful english dictionary

  • riebeckite asbestos — krokidolitas statusas T sritis chemija apibrėžtis Amfibolų grupės pluoštinis mineralas. atitikmenys: angl. crocidolite; riebeckite asbestos rus. крокидолит; рибекитовый асбест ryšiai: sinonimas – ribekito asbestas …   Chemijos terminų aiškinamasis žodynas

  • Riebeckit — Dieser Artikel wurde aufgrund von formalen Mängeln an Gestaltung bzw. Form und/oder inhaltlichen Mängeln auf der Qualitätssicherungsseite des WikiProjekts Minerale eingetragen. Dies geschieht, um die Qualität der Artikel aus dem Themengebiet… …   Deutsch Wikipedia

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