Yoderit

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Yoderit
Yoderite in talc Hydrous magnesium iron aluminum silicate Mautia Hill Central Province tanzania 1938.jpg
General and classification
chemical formula
  • (Al 3 Mg) [6] (Mg, Al, Fe 3+ ) 4 [5] [O | OH | (SiO 4 ) 2 ] 2
  • (MgAl 3 ) (MgAl) Al 2 O 2 (SiO 4 ) 4 (OH) 2
Mineral class
(and possibly department) 		Silicates and Germanates - island silicates
System no. to Strunz
and to Dana 		9.AF.25 ( 8th edition : VIII / B.02)
52.02.02b.03
Similar minerals Kyanite , andalusite
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / m (No. 11)Template: room group / 11
Lattice parameters a  = 8.02  Å ; b  = 5.82 Å; c  = 7.25 Å
β  = 104.9 °
Formula units Z  = 1
Physical Properties
Mohs hardness 6th
Density (g / cm 3 ) measured: 3.39; calculated: [3.33]
Cleavage indistinct after {100}; Secretions according to [001]
colour dark purple, emerald green, red to purple red; in the transparent microscope deep blue or olive green to yellow
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.689 to 1.691
n β  = 1.691 to 1.693
n γ  = 1.712 to 1.715
Birefringence δ = 0.023 to 0.024
Optical character biaxial positive
Axis angle 2V = 25 ° to 30 ° (measured), 34 ° to 36 ° (calculated)
Pleochroism Strong:
X = light Prussian blue, green
Y = indigo blue, light yellow
Z = light olive green , yellow

The mineral yoderite is a very rarely occurring high-pressure, high-temperature orthosilicate from the mineral class of "silicates and germanates" with the chemical composition (Al 3 Mg) [6] (Mg, Al, Fe 3+ ) 4 [5] [O | OH | (SiO 4 ) 2 ] 2 and thus is chemically seen a complex aluminum - magnesium - silicate with additional oxygen - and hydroxide ions . The elements magnesium, aluminum and iron indicated in the second round brackets can represent each other in the formula ( substitution , diadochie), but are always in the same proportion to the other components of the mineral. Structurally , Yoderit belongs to the island silicates .

Yoderite crystallizes in the monoclinic crystal system , but has so far only been found in the form of irregular grains and leafy or lamellar aggregates . The transparent, glass-like shiny crystals can take on a dark purple, emerald green or red to purple color , depending on the amount of foreign matter. In the transmitted light microscope , Yoderite also appears deep blue or olive green to yellow. However, the mineral always leaves a white line on the marking board .

Etymology and history

Yoderit was first discovered on Mautia Hill in the Kongwa district ( Dodoma region ) in Tanzania . It was first described in 1959 by Duncan McKie and AJ Radford, who named the mineral after Schuyler Yoder , Jr., the petrologist and then director of the Geophysical Laboratory at the Carnegie Institution for Science Hatten .

Type material of the mineral is Geological Survey of Tanzania in Dodoma, Tanzania under the catalog no. JH 2563/2 and JH 2563/14 as well as in the National Museum of Natural History in Washington, DC in the USA under catalog no. 137854 kept.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the yoderite belonged to the mineral class of "silicates and germanates" and there to the department of "island silicates with non-tetrahedral anions (Neso subsilicates)", where together with andalusite , Boromullite , Kanonait , Krieselit , Kyanit , Mullit , Sillimanit and Topaz the "Topas group" with the system no. VIII / B.02 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), assigns Yoderit to the class of “silicates and germanates” and there in the department of “island silicates (nesosilicates)”. This is further subdivided according to the possible presence of additional anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the sub-section “Island silicates with additional anions; Cations in [4] er, [5] er and / or only [6] er coordination ”can be found, where it is the only member of the unnamed group 9.AF.25 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Yoderit to the class of "silicates and germanates" and there in the department of "island silicates: SiO4 groups and O, OH, F and H 2 O". Here it is together with andalusite and cannonaite in the " Al 2 SiO 5 (andalusite subgroup) " with system no. 52.02.02b within the subsection " Island silicates: SiO4 groups and O, OH, F and H 2 O with cations in [4] and> [4] coordination".

Chemism

The analysis carried out by AJ Radford and JH Scoon on cleaned samples of the type material JH 2563/2 showed a composition of 36.07 to 36.12% SiO 2 , 0.35% TiO 2 , 41.00 to 41.06% Al 2 O 3 , 0.5% Fe 2 O 3 , 4.81 to 4.82% FeO, 0.32% MnO, 12.21 to 12.23% MgO, 1.48% CaO, 0.01% Na 2 O, 0.05% K 2 O and 3.20% H 2 O + and 0.05% H 2 O - , which corresponds to the corrected empirical composition of (Mg 2.0 Ca 0.2 Fe 0.5 Al 5.3 ) 8.0 Si 4.0 O 17.6 ( OH) corresponds to 2.4 · H 2 O + .

A further analysis of two samples, also from the Mautia Hill type locality in Tanzania, carried out in 1978 by RM Abu-Eid, K. Langer and F. Seifert, showed the slightly different composition of 35.94 to 36.07% SiO 2 , 0.07 to 0.11% TiO 2 , 42.76 to 42.95% Al 2 O 3 , 4.08 to 5.16% Fe 2 O 3 , 0.62 to 0.85% Mn 2 O 3 , 0.19 to 0.24% FeO, 0.13 to 0.23% MnO, 11.83 to 12.05% MgO, 2.69% H 2 O + and 0.36% P 2 O 5 . The resulting empirical composition is (Mg 1.95 Fe 2+ 0.02 Mn 2+ 0.01 ) Σ = 1.98 (Al 5.57 Fe 3+ 0.34 Mn 3+ 0.07 Ti 0.01 ) Σ = 5.99 (Si 3.98 P 0.03 ) Σ = 4.01 O 18.02 ( OH) 1.98 or in the idealized form Mg 2 (Al, Fe 3+ ) 6 Si 4 O 18 (OH) 2 .

More detailed studies of the crystal structure of yoderite, carried out in 1982 by John B. Higgins, Paul H. Ribbe and Yoshiharu Nakajima, finally led to an adapted formula taking into account the structure of the mineral in the notation VI [MgAl 3 ] V [MgAl] V [Al 0.84 Fe 3+ 0.16 ] 2 O 2 (OH) 2 [SiO 4 ] 4 or also (Al 3 Mg) [6] (Mg, Al, Fe 3+ ) 4 [5] [O | OH | (SiO 4 ) 2 ] 2 in the crystal chemical structural formula notation according to Strunz .

Crystal structure

Yoderite crystallizes monoclinically in the space group P 2 1 / m (space group no. 11) with the lattice parameters a  = 8.02  Å ; b  = 5.82 Å; c  = 7.25 Å and β = 104.9 ° as well as one formula unit per unit cell . Template: room group / 11

The crystal structure consists of chains of corner-sharing (Al, Mg) O 5 (OH) octahedra parallel to the b-axis [010]. These are formed by island-like distributed SiO 4 - tetrahedron corner-sharing as well as two, trigonal dipyramids of (Al, Mg, Fe) (O, OH) 5 is connected.

properties

Thin section with differently oriented yoderite grains and clear pleochroism

A striking feature of Yoderit is its strong pleochroism . Depending on the direction from which the light penetrates the crystal, the mineral appears either light Prussian blue or green, indigo blue or light yellow or light olive green or yellow. This property is particularly evident in thin sections under the transmitted light microscope, as the optical axes of the individual grains in the rock structure are aligned differently.

Education and Locations

Yoderite forms as the main phase in quartz - kyanite - talc - schists at a pressure of ≈ 10 kbar H 2 O and a temperature of 800º C. In the samples found so far, yoderite was therefore mostly found grown together with kyanite or growing around it. In addition to the minerals already mentioned, hematite also occurs as accompanying minerals .

So far, apart from its type locality Mautia Hill in Tanzania, only one other site is known (as of 2018), namely the Kadunguri white slate in the Zambezi belt in the Mashonaland of Zimbabwe .

See also

literature

  • Duncan McKie, AJ Radford: Yoderite, a new hydrous magnesium iron alumino-silicate from Mautia Hill, Tanganyika . In: Mineralogical Magazine . tape 32 , 1959, pp. 282–307 ( rruff.info [PDF; 1.5 MB ; accessed on July 2, 2018]).
  • Michael Fleischer : New mineral names . In: American Mineralogist . tape 45 , 1960, pp. 753-756 ( rruff.info [PDF; 289 kB ; accessed on July 5, 2018]).
  • SG Fleet, HD Megaw: The crystal structure of yoderite . In: Acta Crystallographica . tape 15 , 1962, pp. 721-728 , doi : 10.1107 / S0365110X62001930 .
  • RM Abu-Eid, K. Langer, F. Seifert: Optical absorption and Mössbauer spectra of purple and green yoderite, a kyanite-related mineral . In: Physics and Chemistry of Minerals . tape 3 , 1978, p. 271-289 , doi : 10.1007 / BF00633576 .
  • John B. Higgins, Paul H. Ribbe, Yoshiharu Nakajima: An ordering model for the commensurate antiphase structure of yoderite . In: American Mineralogist . tape 67 , no. 1-2 , 1982, pp. 76-84 ( minsocam.org [PDF; 989 kB ; accessed on July 5, 2018]).

Web links

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

Individual evidence

  1. ↑ a b c d e f 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.  548 .
  2. ^ IMA / CNMNC List of Mineral Names; March 2018 ( Memento from June 11, 2018 in the Internet Archive ) (PDF 1.65 MB)
  3. ↑ a b c John B. Higgins, Paul H. Ribbe, Yoshiharu Nakajima: An ordering model for the commensurate antiphase structure of yoderite . In: American Mineralogist . tape 67 , no. 1-2 , 1982, pp. 76-84 ( minsocam.org [PDF; 989 kB ; accessed on July 5, 2018]).
  4. ↑ a b c d e f g h Yoderite . 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]).
  5. ↑ a b Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  676 (first edition: 1891).
  6. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  7. ↑ a b c d e Mindat - Yoderite (English)
  8. ^ Duncan McKie, AJ Radford: Yoderite, a new hydrous magnesium iron alumino-silicate from Mautia Hill, Tanganyika . In: Mineralogical Magazine . tape 32 , 1959, pp. 282–307 ( rruff.info [PDF; 1.5 MB ; accessed on July 2, 2018]).
  9. ↑ Michael Fleischer : New mineral names . In: American Mineralogist . tape  45 , 1960, pp. 753-756 ( rruff.info [PDF; 289 kB ; accessed on July 5, 2018]).
  10. ↑ RM Abu-Eid, K. Langer, F. Seifert: Optical absorption and Mössbauer spectra of purple and green yoderite, a kyanite-related mineral . In: Physics and Chemistry of Minerals . tape 3 , 1978, p. 271-289 , doi : 10.1007 / BF00633576 .
  11. ↑ Mindat - thin section with differently oriented yoderite grains and clear pleochroism
  12. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  693 .
  13. ↑ Find location list for Yoderit in the Mineralienatlas and Mindat