Goldmanite

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Goldmanite
Goldmanite-574336.jpg
Dark green, 4 mm goldmanite crystal group from Rybníček, Okres Pezinok , Bratislava region, Slovakia
General and classification
other names

IMA 1963-003

chemical formula Ca 3 V 3+ 2 Si 3 O 12
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.AD.25 ( 8th edition : 8 / A.08-140)
51.4.3b.4
Similar minerals Uvarowit , Momoiit
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Ia 3 d (No. 230)Template: room group / 230
Lattice parameters a  = 12.011 (natural),
synthetic: 12.070  Å
Formula units Z  = 8
Frequent crystal faces Rhombic dodecahedron {110}, trisoctahedron {221}
Physical Properties
Mohs hardness Please complete!
Density (g / cm 3 ) natural mixed crystal: measured: 3.74; calculated: 3.737 synthetic: 3.765
Cleavage not observed
colour dark green - brownish green
Line color Please complete!
transparency Please complete!
shine Diamond luster
Crystal optics
Refractive index n  1.821 (natural mixed crystal);
1,834 (synthetic)
Birefringence δ = slightly abnormal birefringent

The mineral goldmanite is a rare island silicate from the garnet group and has the idealized chemical composition Ca 3 V 3+ 2 Si 3 O 12 . It crystallizes in the cubic crystal system with the structure of garnet.

Goldmanite forms green to brownish green rhombic dodecahedral or roundish crystals with a diamond luster , which are rarely larger than 1–2 mm. The crystals are often optically weakly birefringent and can have sector zoning.

Garnets rich in goldmanite are formed during the contact metamorphosis of sediments containing vanadium and calcium . The type locality is the Sandy Mine near Laguna in Cibola County , New Mexico , USA .

Etymology and history

Low vanadium contents in calcium grenades have been known since the beginning of the 20th century, and Doelter specified the composition of the vanadium end link with Ca 3 V 3+ 2 Si 3 O 12 in his Handbuch der Mineralchemie as early as 1917 .

The first grenades, the composition of which is dominated by this terminal link, were found in 1962 by Robert H. Moench in the contact metamorphosed uranium - vanadium deposit in the area of ​​the Sandy Mine in Laguna, New Mexico, and in 1964 by Moench and Meyrowitz of the United States Geological Survey described as a new mineral of the garnet group. They chose the name gold namnite in honor of the longtime sedimentologist of the United States Geological Survey, Marcus I. Goldman. At the beginning of the 1940s, he examined the area of ​​the uranium deposit and described the Entrada sandstone in which the vanadium garnet was discovered.

In the year after the first description of goldmanite, BV Mill from the Soviet Union , RGJ Strens from the University of California at Berkeley (USA) and Jun Ito from the University of Tokyo (Japan) succeeded in synthesizing pure goldmanite.

Vanadium-containing grossulare from East Africa became known in the 1970s when they were marketed as a gemstone rarity by Tiffany & Co. in New York under the name tsavorite .

classification

The structural classification of the International Mineralogical Association (IMA) is one of the Goldmanit to Garnet supergroup, where he along with almandine , Andradite , Calderit , Eringait , Grossular , Knorringit , Morimotoit , majorite , Menzerit- (Y) , Momoiit , pyrope , Rubinit , Spessartine and Uvarowite form the garnet group with 12 positive charges on the tetrahedrally coordinated lattice position.

The obsolete, but still used the eighth edition of the mineral classification by Strunz takes the Goldmanit along with almandine, Andradite, Calderit, Grossular, Henritermierit , Hibschite , Holtstamit , Hydrougrandit , katoite , Knorringit, Morimotoit, majorite, pyrope, Schorlomit , Spessartin, Uwarowit, Wadalite and Yamatoite (discredited because they are identical to Momoiite ) in the "garnet group" with the system no. VIII / A.08 within the department of " Island Silicates (Nesosilicates)".

Also the 9th edition of the Strunz'schen mineral systematics, valid since 2001, counts the goldmanite to the "garnet group" with the system no. 9.AD.25 within the department of "Island Silicates (Nesosilicates)". However, this is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates without additional anions; Cations in octahedral [6] and usually greater coordination ”can be found.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns the goldmanite to the section of "island silicate minerals ". Here it is together with Andradit, Grossular, Momoiit (outdated: Yamatoit) and Uwarovite in the "Garnet group (Ugrandite series)" with the system no. 51.04.03b to be found in the subsection “ Island silicates: SiO 4 groups only with cations in [6] and> [6] coordination ”.

Chemism

Goldmanite with the idealized composition [X] Ca 3 [Y] V 3+ [Z] Si 3 O 12 is the vanadium analog of grossular ( [X] Ca 3 [Y] Al [Z] Si 3 O 12 ) or Andradite ( [X] Ca 3 [Y] Fe 3+ [Z] Si 3 O 12 ) with which it forms mixed crystals according to the exchange reactions

  • [Y] V 3+ = [Y] Al 3+ , (grossular)
  • [Y] V 3+ = [Y] Fe 3+ (andradite).

Goldmanite- momoiite mixed crystals have been found in metamorphic manganese deposits in Japan . In these mixed crystals, manganese becomes via the exchange reaction

  • [X] Ca 2+ = [X] Mn 2+

built in goldmanite.

The following composition is given for the goldmanite from the type locality:

  • [X] (Ca 2.91 Mn 0.02 Mg 0.08 ) [Y] (V 3+ 1.20 Al 0.47 Fe 3+ 0.33 ) [Z] Si 2.99 O 12 ,

where [X], [Y] and [Z] indicate the positions in the garnet structure.

In many goldmanites, part of the vanadium has been replaced by chromium (Cr 3+ ), corresponding to the formation of mixed crystals with uwarowite . The proportion of the uwarovite component in goldmanite mixed crystals rarely exceeds 25 mol%.

Almost all of Goldmanit's investigations have assumed that vanadium is completely trivalent vanadium. The investigation of the oxidation state of vanadium in a natural gold manite with X-ray near-edge absorption spectroscopy showed an average valence of 2.56 - 2.62. According to this , 10-40% of the vanadium in goldmanite, which is usually formed under reducing conditions in the presence of carbon , is divalent (V 2+ ).

Crystal structure

Goldmanite crystallizes with cubic symmetry in the space group Ia 3 d (space group no. 230) with 8 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameter a  = 12.011  Å . For synthetic goldmanite, a  = 12.09 Å, a  = 12.070 Å and 12.06 Å, respectively. Template: room group / 230

Like grossular, natural goldmanite is often optically birefringent, which indicates a lower symmetry. Uher et al. State triclinic symmetry in space group I 1 (space group no. 2, position 4) for sector-zoned, anisotropic goldmanite . The triclinic lattice parameters a = 12.003 Å, b = 11.991 Å, c = 12.009 Å, = 90.12 °, ß = 90.04 °, j = 90.04 ° deviate only slightly from the ideal, cubic symmetry. They give the order of the cations on the 8 different octahedral positions of the triclinic structure as the cause of the lowering of symmetry. Template: room group / 2.4

The structure is that of garnet . Magnesium (Ca 2+ ) which occupies dodecahedral of 8 oxygen ions surrounded X positions, vanadium (V 3+ ) the octahedrally by 6 oxygen ions surrounded Y-position and the tetrahedrally by 4 oxygen ions surrounded Z position is exclusively with silicon (Si 4+ ) occupied.

Education and Locations

In low-oxygen conditions, some heavy metals , e.g. B. uranium , vanadium , copper , zinc , complexes with carbon . This can lead to excessive accumulation of these metals in carbon-rich sediments formed under these conditions, e.g. B. black schists . Are such carbonate sediments z. B. heated by contact metamorphosis , goldmanite forms at ~ 500 ° C.

There are only a few documented locations of goldmanite worldwide.

In the type locality , the Sandy Mine near Laguna in New Mexico , goldmannite occurs in thin layers of dark sandstones that have been traversed by diabase dykes and changed by contact metamorphosis. Accompanying minerals are quartz with vanadium-containing mica (presumably roscoelite ), montmorillonite and calcite as cement phases .

The hitherto purest goldmanite (96. Mol%) was recovered from a sandstone from a drill core at a depth of 1902 m in the course of the oil prospecting in the North Sea . This tiny grain of goldmanite is of detritic origin, i.e. it did not grow in the sandstone and nothing is known about its formation conditions.

Comparably pure goldmanite with up to 91 mol% was found in the metamorphically embossed black schists from the Deokpyeong area in the Ogcheon Belt in Korea. The round enema, up to 1.7 mm in size, are green and slightly birefringent. They occur in a matrix of graphite , clinochlor , pyrite , tremolite , celsian and quartz together with small amounts of barite , uranocircite , uraninite , phlogopite , apatite , titanite and talc .

In the Pezinok-Pernek crystalline complex near Pezinok in Okres Pezinok in Bratislavský kraj , Slovakia , goldmanite also occurs in metamorphic black schists. The very fine-grained basic mass of black slate consists of albite , quartz, amphibole, phlogopite, muscovite , chlorite , pumpellyite , titanite, pyrite and organic carbon, which has been converted to metaanthracite to semigraphite . It contains up to 5 mm large, light green garnets with compositions between goldmanite, uvarowite and grossular. The goldmanite content ranges from 16 to 73%.

See also

Web links

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

Individual evidence

  1. ↑ a b c d e f g h i j k l Robert H. Moench and Robert Meyrowitz: Goldmanite, a vanadium garnet from Laguna, New Mexico. In: American Mineralogist . tape 49 , 1964, pp. 644–655 ( rruff.info [PDF; 550 kB ; accessed on February 17, 2018]).
  2. ↑ a b c d e Pavel Uher, Martin Kováčik, Michal Kubiš, Alexander Shtukenberg, and Daniel Ozdín: Metamorphic vanadian-chromian silicate mineralization in carbon-rich amphibole schists from the Malé Karpaty Mountains, Western Carpathians, Slovakia . In: American Mineralogist . tape 93 , no. 1 , 2008, p. 63–73 ( rruff.info [PDF; 2.1 MB ; accessed on February 17, 2018]).
  3. ↑ a b c d e f g h RGJ Strens: Synthesis and properties of calcium vanadium garnet (goldmanite). In: American Mineralogist . tape 50 , 1965, pp. 260 ( minsocam.org [PDF; 64 kB ; accessed on February 17, 2018]).
  4. ↑ a b c d e Jun Ito: Synthesis of Vanadium Silicates: Haradaite, Goldmanite and Roscoelite . In: Mineralogical Journal . tape 4 , no. 4 , 1965, pp. 299–316 ( jst.go.jp [PDF; 2.0 MB ; accessed on February 17, 2018]).
  5. ↑ C. Doelter, P. Jannasch, G. d'Achiardi: Garnet group . In: Handbuch der Mineralchemie . tape 2 , 1917, p. 878-1076 , doi : 10.1007 / 978-3-642-49877-0_25 .
  6. ↑ a b BV Mill ': Hydrothermal Synthesis of Garnets Containing V3 +, In3 + and Sc3 + . In: Soviet Physics Doklady . tape 9 , 1964, pp. 414 .
  7. ↑ Vincent Pardieu and Richard W. Hughes: Tsavorite - the untamed beauty . In: Geology . 2008, p. 36–45 ( researchgate.net [PDF; 675 kB ; accessed on February 18, 2018]).
  8. ^ Edward S. Grew, Andrew J. Locock, Stuart J. Mills, Irina O. Galuskina, Evgeny V. Galuskin and Ulf Hålenius: IMA Report - Nomenclature of the garnet supergroup . In: American Mineralogist . tape 98 , 2013, p. 785–811 ( main.jp [PDF; 2,3 MB ; accessed on July 8, 2017]).
  9. ↑ Michael Fleischer: New Mineral Names: Yamatoite . In: The Amaerican Mineralogist . tape 50 , 1965, pp. 810 ( minsocam.org [PDF; 711 kB ; accessed on February 25, 2018]).
  10. ↑ H. Tanaka, S. Endo, T. Minakawa, M.Enami, D. Nishio-Hamane, H. Miura and A. Hagiwara: Momoiite, (Mn2 +, Ca) 3 (V3 +, Al) 2Si3O12, a new manganese vanadium garnet from Japan . In: Journal of Mineralogical and Petrological Sciences . tape 105 , 2010, p. 92–96 ( jst.go.jp [PDF; 729 kB ; accessed on February 25, 2018]).
  11. ↑ a b Pavel Uher, Martin Chovan, and Juraj Majzlan: anadian-chromian garnet in mafic pyroclastic rocks of the Malé Karpaty Mts., Western Carpathians, Slovakia. In: Canadian Mineralogist . tape 32 , 1994, pp. 319-326 ( researchgate.net [PDF; 852 kB ; accessed on February 17, 2018]).
  12. ↑ K. Righter, S. Sutton, L. Danielson, K. Pando, G. Schmidt, H. Yang, S. Berthet, M. Newville, Y. Choi, RT Downs, and V. Malavergne: The effect of fO2 on the partitioning and valence of V and Cr in garnet / melt pairs and the relation to terrestrial mantle V and Cr content . In: American Mineralogist . tape 96 , 2011, p. 1278–1290 ( rruff.info [PDF; 675 kB ; accessed on February 18, 2018]).
  13. ↑ The numbering of this axis position does not correspond to the order of the International Tables for Crystallography , because it is not listed there.
  14. ↑ Find location list for goldmanite at the Mineralienatlas and at Mindat
  15. ↑ Claire R. Hall Worth, Alec Livingstone and Andrew C. Morton: detrital goldmanite from the Palaeocene of the North Sea . In: MINERALOGICAL MAGAZINE . tape 56 , 1992, pp. 117–120 ( minersoc.org [PDF; 318 kB ; accessed on February 20, 2018]).
  16. ^ GY Jeong and YH Kim: Goldmanite from the black slates of the Ogcheon belt, Korea . In: Mineralogical Magazine . tape 63 , no. 2 , 1999, p. 253–256 ( rruff.info [PDF; 204 kB ; accessed on February 17, 2018]).