Erythrin

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Erythrin
Erythrite-168034.jpg
Group of needle-like, radial-rayed erythrin crystals from Agoudal, Bou Azzer, Tazenakht, Ouarzazate Province , Souss-Massa-Draâ, Morocco (field of view: 8 cm)
General and classification
other names
  • Arsenic acid cobalt or arsenic acid cobalt oxide
  • Coboltum rubrum or Cobaltum rubrum
  • Flos Cobalti
  • Kobold blossom or cobalt blossom
  • Kobolt fitting or cobalt fitting
  • Rhodoite
  • Red earth cobalt
chemical formula Co 3 [AsO 4 ] 2 • 8H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.CE.40 ( 8th edition : VII / C.13)
03/40/06/03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Room group (no.) C 2 / m (No. 12) (No. 12) Template: room group / 12
Lattice parameters a  = 10.25  Å ; b  = 13.45 Å; c  = 4.76 Å
β  = 105.0 °
Formula units Z  = 2
Frequent crystal faces {001}, {010}, {100}, {110}, { 2 21}
Physical Properties
Mohs hardness 1.5 to 2.5
Density (g / cm 3 ) measured: 3.06; calculated: 3.135
Cleavage completely after {010}; indistinct after {100} and {102}
Break ; Tenacity uneven
colour carmine red, peach red, pink, light pink, colorless to white
Line color light red to pink
transparency transparent to translucent
shine Glass gloss, pearlescent gloss
Crystal optics
Refractive indices n α  = 1.626 to 1.629
n β  = 1.662 to 1.663
n γ  = 1.699 to 1.701
Birefringence δ = 0.073
Optical character biaxial positive
Axis angle 2V = 85 to 90 ° (measured); 88 to 90 ° (calculated)
Pleochroism X = light pink to light pink; Y = light purple to light pink-purple; Z = deep red
Other properties
Special features dehydrated erythrin turns lavender blue

Erythrin , out of date also known as Kobold Blossom , Cobalt Blossom and Cobaltum rubrum as well as the color pigment cobalt violet , is a rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates " with the chemical composition Co 3 [AsO 4 ] 2 · 8H 2 O and is therefore chemically a water-containing cobalt arsenate .

Erythrin crystallizes in the monoclinic crystal system and develops mostly small, prismatic, tabular and needle-like crystals in hair -shaped , tufted or radial mineral aggregates as well as spherical-kidney shapes and powdery hues.

The mineral is transparent to translucent and predominantly of the characteristic peach (blossom) red or pink color, but can also be found in darker carmine red or lighter pink . Colorless to white erythrins are also known, but very rare. He leaves a light red to pink line on the whiteboard . Visible crystal surfaces have a glass-like sheen , whereas cleavage surfaces have a more mother-of-pearl shimmer.

With annabergite (Ni 3 [AsO 4 ] 2 · 8H 2 O) and hornsite (Mg 3 [AsO 4 ] 2 · 8H 2 O), erythrin forms a complete series of mixed crystals .

Etymology and history

5 Pfennig stamp with the imprint Erythrin from Schneeberg

Erythrin was named in 1832 by the French mineralogist François Sulpice Beudant after the Greek word ἐρυθρός erythrós for " red ". Beudant also gives cobalt arséniaté and arsenic acid cobalt as synonyms .

A first written mention of the mineral, albeit without a description or location, can be found around 150 years earlier in the anonymous work Mvsævm Brackenhofferianvm published in 1683 under the name Coboltum rubrum or red Kobolt .

It was only in the collection catalog published by Georg Gottfried Richter in 1719 that various mineral samples of the Kobold blossom were also assigned to locations. The samples came from different regions of the Ore Mountains such as Schwarzenberg / Erzgeb. (formerly civitas Swartzenberg ), Schneeberg , the “Beschert Glück” mine near Freiberg and St. Veit near Selva in Saxony; Blankenburg and the tunnel “Charlotte Aufrichtigkeit” on the Roten Berg near Saalfeld in Thuringia as well as Jáchymov (German Joachimsthal ) and the mine “Glücksburg” near Horní Blatná (German mining town Platten ) in today's Czech Republic.

Other well-known synonyms for erythrin include Flos Cobalti (after Johann Theodor Eller , 1723) and Roter Erdkobalt (after Werner ) The term cobalt coating is no longer in use, as it consists of a mixture of erythrin and arsenic acid according to the modern mineral definition .

The earliest known chemical analysis of the mineral comes from Christian Friedrich Bucholz , who carried out it in 1810 using material from Richelsdorf (Germany). At about the same time, Laugier also analyzed a sample from Allemont (France). Jöns Jakob Berzelius calculated the chemical formula Co 3 [AsO 4 ] 2  · 6 H 2 O from the analysis by Bucholz , while the analysis of Laugier resulted in a formula with 9 H 2 O. Another sample from Schneeberg, however, showed a water of crystallization content of only 5 H 2 O.

The contradicting results finally prompted the chemist Carl Kersten to carry out a further and careful analysis with selected, clean material from the Schneeberg mines "Wolfgang Maassen" and "Rappold", which resulted in the formula Co 3 [AsO 4 ] 2 · 8H, which is still valid today 2 O. In a comparison with the composition of annabergite and vivianite (Fe 3 [PO 4 ] 2  · 8H 2 O), Kersten also found the close relationship between the minerals, in whose formula the elements cobalt (erythrin), nickel (annabergite ) and iron (Vivianite) represent each other.

In May 1969, the GDR's Deutsche Post issued a series of special postage stamps with the theme “ Minerals from the Freiberg Mining Academy ”, in which erythrin is also represented.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the erythrin belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "water-containing phosphates without foreign anions", where it belonged together with Annabergit , Arupit , Barićit , Bobierrit , Cattiit , Hörnesit , Köttigit , Manganohörnesit , Parasymplesit and Vivianit the "Vivianite group" with the system no. VII / C.13 formed.

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 erythrin to the class of "phosphates, arsenates and vanadates" and there to the department of "phosphates etc. without additional anions ; with H 2 O “. However, this section is further subdivided according to the size of the cations involved and the molar ratio of phosphate, arsenate or vanadate complex (RO 4 ) to crystal water (H 2 O), so that the mineral is classified in the sub-section “Mit medium-sized cations only; RO 4  : H 2 O ≤ 1 "is found, where it together with Annabergit, Arupit, Barićit, 2.5 Ferrisymplesit , Hörnesit, Köttigit, Manganohörnesit, Pakhomovskyit , Parasymplesit, Santabarbarait and Vivianit the" Vivianit group " . 8 CE.40 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns erythrin to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here he is together with Vivianit, Barićit, Annabergit, Köttigit, Parasymplesit, Hörnesit, Hörnesit and Pakhomovskyit in the "Vivianit-Gruppe" with the system no. 40.03.06 within the sub-section of " Water-containing phosphates etc., with (A 2+ ) 3 (XO 4 ) 2 × x (H 2 O) ".

Crystal structure

Tabular erythrin crystals in visibly monoclinic formation from Agoudal, Bou Azer, Ouarzazate , Morocco (field of view: 3.3 cm)

Erythrin crystallizes isotypically with vivianite in the monoclinic crystal system in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 10.25  Å ; b  = 13.45 Å; c  = 4.76 Å and β = 105.0 ° as well as 2 formula units per unit cell .

properties

When heated, erythrin turns blue, releasing water and arsenic (III) oxide . With acids it forms red solutions.

Education and Locations

Hair-shaped erythrin from the Mountain Cobalt Mine in the Selwyn District , Queensland, Australia (size: 1.6 × 0.9 × 0.6 cm)
Erythrin and stellerite from the Sara Alicia Mine, San Bernardo, Municipio de Alamos, Sonora , Mexico ( total size of the sample: 19.0 × 9.8 × 8.0 cm)
Druse with almost colorless erythrin crystals surrounded by green brochantite from Wheal Edward, St Just mining district, Cornwall , UK (cavity size 2 mm × 1.5 mm)

Erythrite is a typical secondary mineral and formed by oxidation mainly from Skutterudit ( smaltite ), nickel Skutterudit and Cobaltit , but also other arsenic-containing cobalt ores in cobalt - nickel - and uranium - deposits . Depending on the molar ratio of cobalt and nickel, coatings of erythrin or annabergite are created. Accompanying minerals include adamin , cobaltite, roselith-β , malachite , morenosite , pharmacosiderite , retgersite , scorodite , skutterudite and symplesite .

As a rather rare mineral formation, erytrhin can sometimes be abundant at various sites, but overall it is not very common. So far (as of 2012) around 700 sites are known to be known. In addition to the first finds in the Saxon and Czech Ore Mountains as well as in Thuringia, other important sites are Bou Azzer near Tazenakht in the Moroccan province of Ouarzazate , where tabular crystals up to 6 cm long were found.

Other German sites are also in the Black Forest (Baden-Württemberg), in the Hessian Odenwald and Taunus , in the Harz Mountains from Lower Saxony to Saxony-Anhalt to Thuringia and in the Bergisches Land and Sauerland in North Rhine-Westphalia, in the Siegerland and the Eifel from North Rhine-Westphalia to Rhineland-Palatinate.

In Austria, the mineral has so far mainly occurred in Carinthia (Friesach-Hüttenberg, Gailtal and Carnic Alps, Gurktal Alps), Salzburg (Hohe Tauern, Radstädter Tauern, Schwarzleograben / Leogang), Styria (Liesing-Palten-Tal, Schladming), North Tyrol and in Vorarlberg (Montafon).

In Switzerland, only a few sites are known to date in the canton of Valais , including Saint-Luc VS , Mont Chemin and the Turtmann Valley .

Other locations include Argentina, Australia, Azerbaijan, Bolivia, Chile, China, the Democratic Republic of the Congo, France, Greece, India, Iran, Ireland, Italy, Japan, Canada, Korea, Mexico, Norway, Poland, Portugal, Romania, Russia, Sweden, Slovakia, Spain, South Africa, the United Kingdom (Great Britain) and the United States of America (USA).

use

As a cobalt ore , erythrin is rather insignificant, even if it is mined together with other cobalt ores when it is locally accumulated in order to be processed as a raw material in the blue paint works to produce the pigment cobalt violet .

Due to its striking color, however, the mineral is a good indicator when prospecting cobalt deposits, among other things, for primary cobalt arsenides such as skutterudite and cobaltite.

See also

literature

Web links

Commons : Erythrin (Erythrite)  - Collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d Thomas Witzke : The discovery of erythrin at www.strahl.org
  2. ^ A. Himmelbauer, R. Koechlin, A. Marchet, H. Michel, O. Rotky, JE Hibsch: Mineralogisches Taschenbuch der Wiener Mineralogische Gesellschaft . 2nd Edition. Springer, Vienna 1928, p. 53 ( limited preview in Google Book search).
  3. ↑ a b c d e f g Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  481 .
  4. ↑ Webmineral - Erythrite (English)
  5. ↑ a b c Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  636-637 .
  6. ↑ a b c d e f Erythrite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 65  kB ]).
  7. ↑ a b c d e Mindat - Erythrite
  8. ↑ FS Beudant: Érythrine, cobalt arseniates in: Traité de Élémentaire Minéralogie , 2nd edition, Paris 1832, pp 596-597 ( PDF 88.7 kB )
  9. ↑ Anonymous 1683: Mvsævm Brackenhofferianvm, That is / Ordinary description of all / as natural as artful things / Which are in Weyland Mr. Eliae Brackenhoffers / former Dreyzehners in this place instead of Strasbourg / Left Cabinet , Strasbourg, Printed and published by Johann Welpern ( PDF 141.3 kB )
  10. ↑ Georg Gottfried Richter (published under the abbreviation GGR): Gazophylacium sive Catalogus Rerum Mineralium et Metallicarum ut et tam domesticorum qvam exoticorum, varia rudera urbium fructicum, qvo præsentantium una cum qvibusdam petrifactis, et lapidibus, ad regnibus minerale labore collegit / Mineralien-Cabinet Or description of the noblest Ertze / including / many located in Saxony / as well as other foreigners / similarly different things turned into stone, which with great effort / diligence / and expenses / carried together , Freiberg 1719 ( PDF 192, 2 kB )
  11. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 213, 253 (cobalt bloom).
  12. ↑ Mineralienatlas - varieties, synonyms and obsolete names of erythrin
  13. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  643 (first edition: 1891).
  14. ↑ Martin Okrusch, Siegfried Matthes: Mineralogie. 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. 41 .
  15. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 177 .
  16. ↑ Mindat - Localities for Erythrite