Stepanovite

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Stepanovite
General and classification
chemical formula
  • NaMgFe (C 2 O 4 ) 3 • 9H 2 O
  • NaMgFe (C 2 O 4 ) 3 • 8-9H 2 O
  • NaMg (Fe 0.4 Al 0.6 ) (C 2 O 4 ) 3 · 8-9H 2 O
Mineral class
(and possibly department) 		Organic compounds
System no. to Strunz
and to Dana 		10.AB.20 ( 8th edition : IX / A.01)
50.01.07.01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-pyramidal; 3 m
Space group R 3 c (No. 161)Template: room group / 161
Lattice parameters a  = 9.8367  Å ; c  = 36.902 Å
Formula units Z  = 6
Frequent crystal faces {0001}, {11 2 0}, {01 1 2}, {10 1 4}, {51 4 2}
Twinning according to {0001}, observed on synthetic crystals
Physical Properties
Mohs hardness 2
Density (g / cm 3 ) 1.69 (measured); 1.69 (calculated), 1.71
Cleavage no cleavage observed
Break ; Tenacity uneven
colour green, greenish yellow
Line color probably white with shades of green
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.515
n ε  = 1.417
Birefringence δ = 0.098
Optical character uniaxial negative
Pleochroism strong from O = greenish yellow to E = colorless
Other properties
Chemical behavior soluble in H 2 O, the solution has a pH of 5.22

Stepanovite is a very rarely occurring mineral from the mineral class of " organic compounds ". It crystallizes in the trigonal crystal system with the chemical formula NaMgFe (C 2 O 4 ) 3 · 9H 2 O, and is thus chemically seen a crystal water-containing sodium - magnesium - iron - oxalate .

Stepanovit of the type locality is found in thin Gängchen in lignite consisting Xenomorphs granular aggregates and thin solid Gängchen and very rarely of isometric, approximately 0.05 mm wide crystals exist. The mineral comes from the "Tyllakh" lignite deposit in the Lena estuary on the left bank of the Olenekskaya Canal near its mouth, Sakha Republic (Yakutia) , Far East Federal District in Siberia , Russia .

Etymology and history

The Russian mineralogist PI Glushinsky, who found the mineral in 1942, is considered the discoverer of the Stepanovites. Steps recovered in 1949 were examined by Yevgeny Ivanovich Nefedov . Together with VA Mokievskii he published a brief description of the mineral in 1953. The Russian mineralogists Juri N. Knipowitsch , AI Kombow and Evgeni Iwanowitsch Nefedow presented a more detailed description in 1963. Nefedow and Mokievskii named the mineral after the Russian specialist in coal geology Pawel Iwanowitsch Stepanow (1880–1947) from the All-Russian Geological Research Institute (WSEGEI) Alexander Petrovich Karpinsky (WSEGEI) in Leningrad (St. Petersburg) and at the Institute for Geosciences in Moscow .

After these publications, little was published about the new mineral, and the crystal structure of the stepanovite has never been described. It was only in 2016, when it was discovered that the mineral structural similarities with man-made metal-organic frameworks (English: metal-organic frameworks, MOFs), knows which one as magnetic and proton-conductive metal oxalates, which led to a re-examination of Stepanovit ( and the chemically closely related Zhemchuzhnikovit). In the course of this, the information on the physical and crystallographic properties of the mineral were checked and the structure of the mineral clarified.

The type material for Stepanovit is listed under catalog no. 1659/1 kept in the collection of the Mining Institute in St. Petersburg , Russia .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , Stepanovite belonged to the mineral class of "organic compounds" and there to the department of "salts of organic acids", where together with Caoxit , Coskrenit- (Ce) , Glushinskit , Humboldtin , levinsonite (Y) , lindbergite , minguzzite , moolooite , natroxalate , novgorodovaite , oxammite , weddellite , wheatleyite , whewellite , zhemchuzhnikovite and Zugshunstit- (Ce) the independent "group of oxalates " with the system no. IX / A.01 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 Stepanovit to the class of "organic compounds" and there to the department of "salts of organic acids". However, this section is further subdivided according to the type of salt-forming acid , so that the mineral can be found in the sub-section "Oxalates" according to its composition, where it is the only member of the unnamed group 10.AB.20 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Stepanovit to the class of "organic minerals" and there in the department of the same name. Here he is with Zhemchuzhnikovit in the "Stepanovitgruppe" with the system no. 50.01.07 within the sub-section " Salts of organic acids (oxalates) ".

Chemism

Average values from analyzes on Stepanovit led to contents of 4.48% Na, 4.68% Mg, 10.78% Fe 3+ , 50.36% C 2 O 4 and 29.73% H 2 O. The simplified chemical formula for Stepanovit it was given as NaMgFe 3+ (C 2 O 4 ) 3 · 8.5H 2 O, which is 4.42% Na, 4.67% Mg, 10.73% Fe 3+ , 50.75% C 2 O 4 and 29.43% H 2 O requires. The formula has been updated to NaMgFe (C 2 O 4 ) 3 · 9H 2 O.

Crystal structure

Stepanovit crystallizes trigonal in the space group R 3 c (space group no. 161) with the lattice parameters a  = 9.8367  Å and c  = 36.902 Å as well as six formula units per unit cell . Template: room group / 161

The structure of the stepanovite consists of anionic honeycomb-like [NaFe (C 2 O 4 ) 3 ] 2− layers, each layer having openings (apertures) of ≈ 0.9 nm in diameter. The cavities of each layer are occupied by Mg (H 2 O) 6 2+ , which are linked to the oxalate groups lining the pores via hydrogen bonds. In each layer Fe 3+ and Na + adopt octahedrally coordinated environments of opposite chirality (enantiomorphism). The layers are separated from each other by water molecules, each of which forms four hydrogen bonds: two as a donor to the oxalate ions in adjacent layers and two as an acceptor to the guest molecule Mg (H 2 O) 6 2+ in the adjacent layers. The hydrogen bonds around each water molecule form a tetrahedron which is stretched in the crystallographic c-direction [001].

Artificially produced MOFs consist of open [M I M III (C 2 O 4 ) 3 ] 2− framework structures with a three- or two-dimensional network topology (honeycomb topology ), monovalent (M I ; e.g. Li + or Na + ) and trivalent (M III ; e.g. Cr 3+ or Fe 3+ ) cations as network nodes and divalent cations that are retained in the network cavities. Recently, similar metal oxalate structures based on zinc or other transition metals have become interesting as ferromagnetic and / or proton-conducting materials.

properties

morphology

Stepanovit forms xenomorphic, granular aggregates, thin, massive tunnels and, very rarely, isometric, approx. 0.05 mm large crystals in lignite . Synthetic crystals are rhombohedral or hexagonal-prismatic. The supporting forms are the rhombohedra {01 1 2} and {10 1 4}, the crystal costume is completed by the base pinacoid {0001}, the prism {11 2 0} and {51 4 2}. Synthetic crystals can be twinned according to {0001}.

physical and chemical properties

The crystals and aggregates of Stepanovite are greenish yellow to green. The line color is not specified, but the powder color of the green to yellow-green crystals should be a greenish white. The surfaces of the transparent crystals show a clear glass-like sheen . Stepanovit has very low to low refraction and very high birefringence.

The mineral shows no cleavage , but breaks like amblygonite , with the fracture surfaces being uneven. Stepanovit has a Mohs hardness of 2 and is one of the soft minerals that, like the reference mineral plaster, can be scratched with the fingernail. The measured density for Stepanovit is 1.69 g / cm³, the calculated density is also 1.69 g / cm³.

Stepanovite is difficult to melt. In contrast, it is easily soluble in water and can be recrystallized from the solution. The pH of the solution is 5.22.

Education and Locations

As a very rare mineral formation, Stepanovit could so far (as of 2016) only be described from three sites. Its type locality is the “Tyllakh” lignite deposit in the estuary of the Lena River on the left bank of the Olenekskaya Canal near its mouth, former Okrug Bulunski , federal subject Republic Sakha (Yakutia) , Federal District Far East in Siberia , Russia . The type material consists of lignite saturated with ethanoic acid . Accompanying minerals are calcite and dolomite , other natural salts of organic acids such as B. Oxalates (Whewellit, Weddellite and Glushinskit) as well as undefined acetates .

The second site is the "Chai-Tumus" (Tschaitumususk) lignite deposit, 200 km south of the Lena estuary, where stepanovite occurs in lignite saturated with natural ethanoic acid and is accompanied by zhemchuzhnikovite, among others.

The third place of discovery is Norilsk on the Taimyr Peninsula , Putorana Plateau , Taimyrski (Dolgano-Nenezki) Rajon, federal subject of the Krasnoyarsk Region , also in Russia - but without any precise details as to which part of the gigantic deposit the mineral comes from.

use

Due to its rarity, Stepanovit has so far only been of interest to mineral collectors. Since the structures of Stepanovit (and Zhemchuzhnikovit) with their almost nanometer-wide openings and channels and their porous structure correspond to those of synthetically produced MOFs, it is now hoped to find more MOF-like crystals in nature that occur more frequently than the minerals examined Zhemchuzhnikovit and Stepanovit and can therefore be used industrially. The organometallic framework structures (MOF) are coveted materials when it comes to storing and transporting gases (such as hydrogen and carbon dioxide ) as well as separating or catalyzing gaseous mixtures. MOFs can efficiently store and release hydrogen. They were also tested as filter material for the separation of carbon dioxide. Due to their porous structure with large surfaces of up to 4500 m² per gram, MOFs could also be of interest as efficient catalysts.

See also

literature

  • Stepanovit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 52 kB )
  • Juri N. Knipowitsch, AI Kombow and Evgeni Iwanowitsch Nefedow: On stepanovite and the new mineral zhemchuzhnikovite (in Russian) . In: Trudy. Vses. Nauchno-Issled. Geol. Inst. Band 96 , 1963, pp. 131-135 .
  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 798 (first edition: 1891).
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 720 .

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n Igor Huskić, Igor V. Pekov, Sergey V. Krivovichev, Tomislav Friščić: Minerals with metal-organic framework structures . In: Science Advances . 2 (No. 8), 2016, p. e1600621 , doi : 10.1126 / sciadv.1600621 ( advances.sciencemag.org [PDF; 793 kB ]).
  2. ^ 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.  718 .
  3. ↑ a b c d e f g h i j Juri N. Knipowitsch, AI Kombow and Evgeni Iwanowitsch Nefedow: On stepanovite and the new mineral zhemchuzhnikovite (in Russian) . In: Trudy. Vses. Nauchno-Issled. Geol. Inst. (WSEGEI) . tape 96 , 1963, pp. 131-135 .
  4. ↑ a b c d e Stepanovit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 52 kB )
  5. ^ A b Igor V. Pekov: Minerals first discovered on the territory of the former Soviet Union . 1st edition. Ocean Pictures, Moscow 1998, ISBN 5-900395-16-2 , pp. 241 .
  6. ↑ Yevgeny Ivanovich Nefedov, VA Mokievskii: Information about discovery of new minerals at the Scientific session of the Fedorov Institute together with the All-Union Mineralogical Society . In: Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva . 82 (No. 4), 1953, p. 311-317 .
  7. ↑ Mindat - Number of localities for Stepanovit
  8. ↑ a b List of locations for Stepanovit in the Mineralienatlas and Mindat
  9. ^ A b Jan Oliver Löfken: "Natural metal-organic frameworks discovered". In: World of Physics. Status: August 5, 2016. http://www.weltderphysik.de/gebiet/stoffe/news/2016/natuerliche-metallorganische-gerueste-entdeck/ (accessed on September 7, 2016).
  10. ↑ a b Manfred Lindinger: "Natural MOFs: Airy Crystals from the Heart of Nature". In: Frankfurter Allgemeine Zeitung. Status: August 23, 2016. http://www.faz.net/aktuell/wissen/physik-mehr/luftige-kristalle-forschergruppe-entdeck-mofs-in-mineralien-14389805.html (accessed on September 7, 2016) .