Riebeckite

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Riebeckite
Crystals of black riebeckite in alkaline pegmatite, near Évisa (Corsica, France) .jpg
Black riebeckite crystals in alkali pegmatite near Évisa in the canton of Les Deux-Sevi , Corsica, France
General and classification
chemical formula □ Na 2 Fe 2+ 3 Fe 3+ 2 [(OH) 2 | Si 8 O 22 ]
Mineral class
(and possibly department) 		Silicates and germanates - chain silicates and band silicates
System no. to Strunz
and to Dana 		9.DE.25 ( 8th edition : VIII / F.08)
66.01.03c.05
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 9.81  Å ; b  = 18.01 Å; c  = 5.33 Å
β  = 103.7 °
Formula units Z  = 2
Frequent crystal faces {110}, {010}, { 1 01}
Twinning single or multiple // {100}
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) measured: 3.28 to 3.44; calculated: 3.380
Cleavage completely after {110}
Break ; Tenacity shell-like to uneven; brittle
colour black to dark blue; dark blue to yellow green in thin layers
Line color blue-gray
transparency translucent to opaque
shine Glass gloss to silk gloss
Crystal optics
Refractive indices n α  = 1.680 to 1.698
n β  = 1.683 to 1.700
n γ  = 1.685 to 1.706
Birefringence δ = 0.005 to 0.008
Optical character biaxial negative
Axis angle 2V = 68 to 85 ° (measured), 62 to 78 ° (calculated)
Pleochroism green-blue, gray-blue, yellow-brown

The mineral Riebeckite (Abriachanit, Osanit, Osannit, blue asbestos) is a rarely occurring chain silicate from the group of alkali amphibole . It crystallizes in the monoclinic crystal system with the composition □ Na 2 Fe 2+ 3 Fe 3+ 2 [(OH) 2 | Si 8 O 22 ], so from a chemical point of view it is a complex composed of sodium - iron- silicate, whereby the structural site of sodium ( symbolized by □) is not completely occupied.

Riebeckite rarely develops long, prismatic crystals , which can then be up to 20 cm long. It is generally found in the form of fine-needle to fibrous mineral aggregates , which are known as crocidolite . The translucent to opaque mineral is usually black to dark blue, in thin layers also dark blue to yellow-green in color. Riebeckit leaves a blue-gray line on the marking board . Visible crystal surfaces have a glass-like sheen , while fibrous varieties shimmer like silk .

With magnesia beckite □ Na 2 (Mg, Fe) 3 Fe 3+ 2 [(OH) 2 | Si 8 O 22 ], riebeckite forms a complete mixed crystal row .

Etymology and history

Riebeckite was first discovered by the German ethnologist, mineralogist and natural scientist Emil Riebeck (1853–1885) in the Socotra Archipelago ( Socotra ) in Yemen and described in 1888 by Adolf Sauer , who named the mineral after its discoverer.

classification

Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the riebeckite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it belongs together with Arfvedsonit , Crossit , Dellaventurait , Eckermannit , Ferrinybøit , ferric Ferronybøit , Ferripedrizit , Ferriwhittackerit , Ferro-Eckermannit , Ferroleakeit , Ferroglaukophan , fluoro Ferroleakeit , fluoro-magnesio-Arfvedsonit , Fluoronybøit , Glaukophan , Kaliumarfvedsonit , Kaliumleakeit , Kornit , Kozulith , Leakeit , Magnesio-Arfvedsonit , Magnesioriebeckite , Sodium-Ferri-Ferropedric , Sodium-Ferripedric , Nybøit , Obertiit and Ungarettiit form the independent "amphibole group, subgroup alkali amphiboles" with the system no. VIII / F.08 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns riebeckite to the class of "silicates and germanates" and there in the department of "chain and band silicates (inosilicates)" a. This department is, however, further subdivided according to the type of chain or band structure and partly according to the affiliation to particular mineral relationships, so that the mineral according to its composition in the subdivision “Chain and band silicates with 2-periodic double chains, Si 4 O 11 ; Amphibole family, Klinoamphibole "is to find where it along with Arfvedsonit, Dellaventurait, Eckermannit, ferric Ferronybøit, ferric Klinoferroholmquistit, Ferrinybøit, ferric Ottoliniit , Ferriwhittakerit, Ferro-Eckermannit, Ferroglaukophan, Ferroleakeit, Ferronybøit , Ferropedrizit , fluorine Arfvedsonite , Fluoro-Ferroleakeit, Fluoro-Potassium-Magnesio-Arfvedsoni, Fluoro-Magnesio-Arfvedsonite, Fluoro-Sodium Pedrizite, Fluoronybøit, Fluor-Riebeckit, Glaukophan, Klinoferroholmquistit, Kornit, Kôzulith, Leakeit, Magnesio-Arfioritsonite, Ottoliniit, Pedrizit, Kalium-Magnesio-Arfvedsonit, Kaliumarfvedsonit, Kaliumleakeit, Sodium-Ferri-Klinoferroholmquistit, Sodium-Ferri-Ferropedicit, Sodium-Ferripedic, Sodium-Ferropedric, Sodium-Pedricit, Ungarettiit and Whittakerit the "Alkali-Clino-Amphibole" group., “With the system no. 9.DE.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns it to the class of "silicates and Germanates", but there it is in the more finely divided division of "chain silicates: double unbranched chains, W = 2". Here he is the only member / together with in the "Group 4, sodium amphiboles" with the system no. 66.01.03c within the subsection of " Chain Silicates: Double unbranched chains, W = 2 amphibole configuration ".

Crystal structure

Riebeckite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 9.81  Å ; b  = 18.01 Å; c  = 5.33 Å and β = 103.7 ° as well as 2 formula units per unit cell . Template: room group / 12

Modifications and varieties

Silky crocidolite

The only known variety is crocidolite (also known as hornblende asbestos or blue asbestos ).

Education and Locations

Fibrous "flakes" of riebeckite from the Poudrette quarry, Mont Saint-Hilaire, Québec, Canada (field of view ~ 4.5 × 5.7 mm)
Riebeckite with calcite, dolomite and donnayite from the Poudrette quarry, Mont Saint-Hilaire, Québec, Canada (field of view ~ 4.5 cm wide)

Riebeckite forms either igneously in granite , rhyolite and syenite , where it is mostly found in paragenesis with aegirine , nepheline , albite or arfvedsonite , or associated with tremolite and ferro-actinolite in metamorphic rocks such as quartzites or iron-rich slates . Other accompanying minerals include grunerite , magnetite , hematite , stilpnomelane , anchorite , siderite , calcite .

In the event of weathering through oxidation and partial replacement of the Riebeckite by silicon dioxide ( silicification ), the mineral changes over time to the falcon's eye variety and finally to the tiger eye variety .

As a rather rare mineral formation, riebeckite can sometimes be abundant at different sites, but overall it is not very common. Around 300 sites are known to date (as of 2011).

Khangay in Mongolia , where crystals of up to 15 cm in length came to light, are known for the extraordinary finds of Riebeckite . In the United States, there is the Great Blue Hill, a mountain named after the bluish shimmer of its granite rock, which contains riebeckite.

The only known site in Austria so far is the Schlossberg near Gloggnitz in the industrial district of Lower Austria. In Switzerland, riebeckite was found on Glärnisch in the canton of Glarus, on Piz Lunghin , Plaun Grand (near Sils in Engadin / Segl ) and Kistenpass in the canton of Graubünden, as well as on the Urner Boden and near Ängisort (near Seedorf UR ) in the canton of Uri.

Other locations include Algeria, Antarctica, Argentina, Australia ( e.g. Wittenoom ), Bolivia, Brazil, China, France, Greenland, India, Israel, Italy, Jamaica, Japan, Yemen, Canada, Kazakhstan, Kenya, Kyrgyzstan , Madagascar, Malawi, Mongolia, Namibia, New Zealand, Niger, Nigeria, North Korea, Norway, Pakistan, Portugal, Réunion, Russia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Spain, South Africa, Tajikistan, Ukraine, Hungary, Venezuela, im United Kingdom (Great Britain, including Ailsa Craig ) and the United States (USA).

use

The fibrous variety crocidolite was of technical importance as “ asbestos ” because it can be spun easily and, like the other types of asbestos, is heat and acid-resistant. Due to the severe health risks posed by the fine asbestos fibers, crocidolite asbestos is no longer used.

See also

Individual evidence

  1. ↑ a b c d e f Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  632 .
  2. ↑ Webmineral - riebeckite.
  3. ^ A b Walter Schumann: The great BLV stone and mineral guide . 7th edition. BLV Buchverlag GmbH & Co.KG, Munich 2007, ISBN 978-3-8354-0212-6 , p. 86 .
  4. ↑ a b c d e John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Riebeckite. In: Handbook of Mineralogy, Mineralogical Society of America. 2001 ( handbookofmineralogy.org PDF; 79.1 kB).
  5. ↑ a b c d e f Mindat - Riebeckite.
  6. ↑ Adolf Sauer: About Riebeckit, a new member of the Hornblende group, as well as about new formation of albite in granitic orthoclases , in: Journal of the German Geological Society. Volume 15, Wilhelm Hertz (Bessersche Buchhandlung), Berlin 1888, pp. 138–152 ( rruff.info PDF; 1.2 MB).
  7. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 241 ( Dörfler Natur ).
  8. ↑ Mindat - Localities for riebeckite.

literature

  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 729 (first edition: 1891).
  • Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th fully revised and updated edition. Springer Verlag, Berlin et al. 2005, ISBN 3-540-23812-3 , pp. 99 .

Web links

Commons : Riebeckite  - collection of images, videos and audio files