Rhönit

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Rhönit
Rhönite-620201.jpg
Reddish rhönite crystals on matrix from the Nickenicher Sattel , Nickenich in the Eifel, Rhineland-Palatinate, Germany (length of the largest crystal: 0.16 mm)
General and classification
chemical formula Ca 2 (Mg, Fe 2+ ) 4 TiFe 3+ [O 2 | Al 3 Si 3 O 18 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DH.45 ( 8th edition : VIII / D.07)
69.02.01a.05
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 10.43  Å ; b  = 10.81 Å; c  = 8.93 Å
α  = 105.9 °; β  = 96.1 °; γ  = 124.8 °
Formula units Z  = 2
Twinning polysynthetic parallel {010}
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) measured: 3.4 to 3.76; calculated: [3.64]
Cleavage good after {010} and {001}
Break ; Tenacity not defined
colour brown-red, dark brown to black
Line color red-brown
transparency translucent to opaque
shine Semi-metallic luster
radioactivity available, but hardly measurable
Crystal optics
Refractive indices n α  = 1.795 to 1.810
n β  = 1.806 to 1.825
n γ  = 1.830 to 1.845
Birefringence δ = 0.035
Optical character biaxial positive
Axis angle 2V = 50 ° to 90 ° (measured), 70 ° to 84 ° (calculated)

Rhönite is a seldom occurring mineral from the division of chain silicates and band silicates (inosilicates) within the mineral class of "silicates and germanates". It crystallizes in the triclinic crystal system with the chemical composition Ca 2 (Mg, Fe 2+ ) 4 TiFe 3+ [O 2 | Al 3 Si 3 O 18 ] and is therefore a complex aluminosilicate with additional oxygen ions and the cations calcium , magnesium , titanium and iron in the 3+ oxidation state . The magnesium contained in the formula can also be partially replaced ( substituted ) by iron in the 2+ oxidation state , which is indicated by the round brackets around the two elements.

Rhönite develops tabular to prismatic crystals up to a few centimeters in length, but is also found in the form of skeletal to irregular grains and in mineral aggregates . The translucent to opaque crystals can be brown-red or dark brown to black in color and have a semi-metallic sheen on the surfaces .

Etymology and history

As an independent mineral, Rhönite was described in 1907 in rocks from the Black Mountains of the South Rhön by Julius Soellner (1874-1946), who discovered the mineral in the eponymous Rhön , a low mountain range on the border between the German states of Bavaria , Hesse and Thuringia . Soellner had already described the corresponding rock deposits in 1902, but wrongly identified the mineral as the chromium-containing spinel picotite . In 1906 he corrected this mistake in a publication, but now considered the mineral to be aenigmatite .

As early as 1883, a description of the mineral as the decay product of basaltic hornblende in basalt rocks from the Rhön was published, although it was left open whether this would be a new mineral or merely a new formation of hornblende, as the analyzes available at that time were still available did not allow a definite statement about the nature of the mineral.

classification

Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the Rhönite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it belonged together with aenigmatite , deerite , hainite , Howieit , Magbasit and Tinaksit the "aenigmatite group" with the system no. VIII / D.07 .

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VIII / F.14-50 . In the “Lapis systematics” this also corresponds to the section “Chain and band silicones ” (branched chains), where Rhönit together with Addibischoffit , Aenigmatit, Dorrit , Høgtuvait , Khesinit , Krinovit , Kuratit , Makarochkinit , Serendibit , Warkit , Welshit and Wilkinsonit the "aenigmatite group" forms.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies the Rhönite in the "chain and band silicates" department. This is, however, further subdivided according to the structure of the chains, so that the mineral can be found according to its structure in the subsection "Chain and band silicates with 4-periodic single chains, Si 4 O 12 ", where it can be found together with aenigmatite, baycovite , dorrite , Høgtuvait, Khmaralith , Krinovit, Makarochkinit, Sapphirin , Serendibit, Welshit and Wilkinsonit form the unnamed group 9.DH.45 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Rhönite to the class of "silicates and Germanates" and there in the department of "chain silicates: chains with side branches or loops". Here it is in the " aenigmatite and related species (aenigmatite subgroup) " with the system no. 69.02.01a can be found in the subsection "Chain silicates: chains with side branches or loops with P> 2".

Crystal structure

Rhönite crystallizes triclinic in the space group P 1 (space group no. 2) with the lattice parameters a  = 10.43  Å ; b  = 10.81 Å; c  = 8.93 Å; α = 105.9 °; β = 96.1 ° and γ = 124.8 ° as well as two formula units per unit cell . Template: room group / 2

Education and Locations

Rhönite forms either primarily in silicon-undersaturated, alkaline and mafic , igneous rocks or secondarily through opacitization of amphiboles . Another formation possibility exists in the contact zone between alkaline basalts and limestones . As Begleitminerale among other titaniferous can augite , diopside , various alkaline feldspars , forsterite , Kaersutite , titaniferous magnetite , Magnesioferrit , perovskite and spinel occur.

As a rare mineral formation, Rhönite could only be detected at a few sites, although around 40 sites are known to date (as of 2015). In addition to its type locality in the Rhön near Fulda , the mineral was also found in Germany in a basalt quarry near Gonterskirchen in the Vogelsberg in Hesse, near Scharnhausen in Baden-Württemberg and in several places in the Rhineland-Palatinate Volcanic Eifel . These include the Nickenicher Sattel and Tönchesberg in the Andernach district , the Nerother Kopf and Emmelberg near Üdersdorf in the Daun district , the Niveligsberg in the Drees district , the "Caspar" quarry on the Ettringer Bellerberg , the Kunkskopf and the Veitskopf in the Wassenach community as well as the pus heads , the Karmelenberg and the tub heads in the municipality of Ochtendung .

The only known site in Austria so far is a basalt quarry on Pauliberg in central Burgenland .

Other locations are among others on the Hut Point Peninsula and Mount Sidley in Antarctica; in a quarry west of Scottsdale on the Australian island of Tasmania ; in the French communes of Murol , Alissas and Freyssenet ; on Arnold Escher's land in Tunu County , Greenland; in the Karancs - Medves region ( Northern Hungarian Central Mountains ) and in the Balaton Highlands in Hungary ; on Mount Etna on the Italian island of Sicily ; on Dogo Island in Shimane Prefecture , Japan ; at "Pulling Point" near Dunedin on the South Island of New Zealand ; in Okres Lučenec and in Okres Rimavská Sobota in Slovakia; in the basanite - lava fields El Sebadal and La Isleta near the city of Las Palmas in Gran Canaria in Spain; in the River Ranch Mine near Beitbridge in Zimbabwe as well as on the island of Kauaʻi (Hawaii) and at the discovery point "159" in Big Bend National Park (Texas) in the United States of America.

Furthermore Rhönit was in various meteorites detected as the at D'Orbigny in the Argentine province of Buenos Aires discovered stony meteorites (D'Orbigny meteorite) , which in Pavlodar region in Kazakhstan fallen Efremovka meteorite , which in de Pueblito Allende in the Mexican state Chihuahua felled Allende meteorite , the stone meteorite "NWA 4590" that fell in the Moroccan province of Zagora and the stone meteorite 99555 that fell in the Sahara .

See also

literature

  • J. Soellner: About Rhönite, a new änigmatite-like mineral and about the occurrence and distribution of the same in basaltic rocks . In: New Yearbook for Mineralogy, Geology and Palaontology . tape 24 , 1907, pp. 475-547 ( rruff.info [PDF; 22.6 MB ; accessed on July 19, 2019]).

Web links

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

Individual evidence

  1. ↑ a b c d 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.  644 (English).
  2. ↑ a b c d e Rhönite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 78  kB ; accessed on July 19, 2019]).
  3. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  4. ↑ David Barthelmy: Rhonite MineralData. In: webmineral.com. Accessed July 19, 2019 .
  5. ↑ a b c d e Rhönite. In: mindat.org. Hudson Institute of Mineralogy, accessed July 19, 2019 .
  6. ↑ J. Soellner: About Rhönite, a new änigmatite-like mineral and about the occurrence and distribution of the same in basaltic rocks . In: New Yearbook for Mineralogy, Geology and Palaontology . tape 24 , 1907, pp. 475-547 ( rruff.info [PDF; 22.6 MB ; accessed on July 19, 2019]).
  7. ↑ Julius Soellner: Geognostic description of the Black Mountains in the southern Rhön . In: Yearbook of the Royal Prussian State Geological Institute . tape 22 , 1901, pp. 1-77 ( available online at archive.org  - Internet Archive [accessed July 19, 2019]).
  8. ↑ Literature by and about Soellner, Julius Hubert in the catalog of the German National Library
  9. ^ Author Soellner, Julius, b. 1874. In: franklin.library.upenn.edu. University of Pennsylvania (Penn Libraries), accessed July 19, 2019 .
  10. ↑ Julius Soellner: About the occurrence and distribution of aenigmatite in basaltic rocks . In: Centralblatt für Mineralogie, Geologie und Paläontologie . 1906, p. 206–208 ( PDF on ZOBODAT [accessed July 19, 2019]).
  11. ^ Karl Petzold: Petrographic studies on basalt rocks of the Rhön . Gebauer-Schwetschke'sche Buchhandlung, Halle a. P. 1883, p. 28–29 ( available online at archive.org  - Internet Archive [accessed July 19, 2019]).
  12. ^ Karl Hugo Strunz , Christel Tennyson : Mineralogical tables . 8th edition. Academic publishing company Geest & Portig KG, Leipzig 1982, p.  421 .
  13. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 25, 2019 .
  14. ↑ Localities for Rhönite. In: mindat.org. Hudson Institute of Mineralogy, accessed July 19, 2019 .
  15. ↑ a b c List of localities for Rhönite in the Mineralienatlas and Mindat , accessed on July 19, 2019.