Giniit

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Giniit
General and classification
other names

IMA 1977-017

chemical formula
  • Fe 2+ Fe 3+ 4 (PO 4 ) 4 (OH) 2 · 2H 2 O
  • Fe 2+ Fe 3+ 4 (PO 4 ) 4 (OH) 5 · 2H 2 O
  • Fe 2+ Fe 3+ 4 [(H 2 O) 2 | (OH) 2 | (PO 4 ) 4 ]
  • Fe 2+ Fe 3+ 4 [(OH) 2 | (PO 4 ) 4 ] • 2H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.DB.50 ( 8th edition : VII / D.03)
11/22/07/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 / a (No. 13, position 3)Template: room group / 13.3
Lattice parameters a  = 14.253  Å ; b  = 5.152 Å; c  = 10.353 Å
β  = 111.30 °
Formula units Z  = 2
Frequent crystal faces {100}, {201}, {210}, {103}, {010}
Twinning often knee twins and penetration twins according to { 1 12}
Physical Properties
Mohs hardness 3 to 4
Density (g / cm 3 ) 3.41 (measured); 3.42 (calculated)
Cleavage none observed
Break ; Tenacity shell-like to half-shell; brittle
colour blackish green to blackish brown
Line color olive green
transparency only translucent in thin splinters
shine Glass to fat gloss, diamond to semi-diamond gloss
Crystal optics
Refractive indices n α  = 1.775
n β  = 1.803
n γ  = 1.812
Birefringence δ = 0.037
Optical character biaxial negative
Axis angle 2V = ≈ 55 ° (measured), 58 ° (calculated)
Pleochroism strong from X = light brown to Y = dark brown to Z = dark blue-green
Other properties
Chemical behavior hardly soluble in hot HNO 3 and hot HCl

Giniit is a very rare mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical composition of Fe 2+ Fe 3+ 4 (PO 4 ) 4 (OH) 2 · 2H 2 O and is therefore chemically seen a hydrous iron - phosphate with additional hydroxide .

Giniit developed on its type locality stretched after the b-axis and dicktafelige by {100} crystals which are almost always twinned, in corroded triphylite and Barbosalith sit and there from Hureaulith , Tavorit , Leukophosphit , whitlockite and monetite be accompanied. The type locality of the mineral is the pegmatite of Sandamap on the farm Sandamap North 115 near Usakos , Daures in the Erongo region , Namibia .

Etymology and history

As the discoverer of Giniits applies Walter Kahn , the professor of the test material mineralogy and crystallography at the University of Stuttgart , Paul Keller showed. Keller carried out the investigations necessary for characterization as a new mineral and presented the results to the International Mineralogical Association (IMA), which it recognized in 1977 under the provisional designation IMA 1977-017. In 1980 it was described by Paul Keller in the German science magazine “New Yearbook for Mineralogy, Monthly Issues” as Giniit ( English Giniite ). The author named the mineral after his wife Adelheid "Gini" Keller (* 1940), who supported his mineralogical work in "various ways".

The type material for Giniit (holotype) is kept at the University of Stuttgart (location TM-77.17 / 0/824-s27 / 2).

In the same year as the first publication, Keller corrected the crystallographic information on Giniite in a supplementary work.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the giniite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "water-containing phosphates with foreign anions", where together with gladiusite , kaluginite , Landesit and Schoonerit formed the unnamed group VII / D.03 .

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 Giniit to the class of “phosphates, arsenates and vanadates” and there to the department of “phosphates, etc. with additional anions ; with H 2 O “. However, this section is further subdivided according to the relative size of the cations involved and the molar ratio of the other anions to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral can be classified in the sub-section “With only medium-sized cations; (OH etc.): RO 4  <1: 1 “is to be found where the unnamed group with the system no. 8.DB.50 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Giniit to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc., with hydroxyl or halogen". Here he is to be found as the sole member of the unnamed group 11/22/07 within the subdivision of " Water-containing phosphates etc., with hydroxyl or halogen with (AB) 4 (XO 4 ) 3 Z q × x (H 2 O) ".

Chemism

Microprobe analyzes on Giniit from the “Sandamap pegmatite” showed mean values ​​of 0.68% MgO; 0.63% MnO; 46.07% Fe 2 O 3 ; 1.20% Al 2 O 3 ; 36.99% P 2 O 5 and 6.45% H 2 O ( determined thermogravimetrically ). Pleochroism and microchemical analyzes confirm that iron occurs in Giniit in the form of both Fe 2+ and Fe 3+ ions. A formula of (Fe 2+ , Mg, Mn 2+ ) (Fe 3+ , Al) 4 (PO 4 ) 4 (OH) 2 · 2H 2 O or simplified Fe 2+ Fe 3+ 4 (PO 4 ) 4 (OH) 2 · 2H 2 O, the contents of 9.85% FeO; 43.80% Fe 2 O 3 ; 38.94 P 2 O 5 and 7.41% H 2 O required.

Giniit is the analogue of Whitmoreit with less water of crystallization and / or hydroxyl water , Fe 2+ Fe 3+ 2 (PO 4 ) 2 (OH) 2 · 4H 2 O, Ferrostrunzite , Fe 2+ Fe 3+ 2 (PO 4 ) 2 (OH ) 2 · 6H 2 O, Beraunit , Fe 2+ Fe 3+ 5 (PO 4 ) 4 (OH) 5 · 6H 2 O, and Metavivianit , Fe 2+ Fe 3+ 2 (PO 4 ) 2 (OH) 2 · 6H 2 O.

Crystal structure

Giniit crystallizes in the monoclinic crystal system in the space group P 2 / a (space group no. 13, position 3) with the lattice parameters a  = 14.253  Å ; b  = 5.152 Å; c  = 10.353 Å and β = 111.30 ° as well as two formula units per unit cellTemplate: room group / 13.3

The crystal structure of a synthetic Giniit equivalent consists of an open, cross-linked skeleton of [Fe 5 P 4 O 20 H 4 ] 6- ions with oktedrisch coordinated iron atoms and tetrahedrally coordinated phosphorus -atoms. Results from Mössbauer spectroscopy have shown the positions of three Fe 2+ ions. The anion [Fe 5 P 4 O 20 H 4 ] 6− has a twofold axis of rotation (digyre) and contains two water molecules coordinated with the two equivalent Fe 2+ atoms, which protrude from the cavity formed by the other three oxygen atoms . Although only three hydrogen atoms were found in the structural analysis, the thermogravimetric analysis shows a weight loss that is consistent with the structural formula Fe 5 H 2 (PO4) 4 · 4H 2 O. A noticeable number of channels run in the direction of the c-axis. Two sets of small channels running roughly parallel to the b-axis are also provided. A third set of small channels can be observed by rotating around the c-sinβ axis.

properties

morphology

At its type locality in the "Sandamap pegmatite", Giniit always develops idiomorphic crystals , stretched along the b axis [010] and thick tabular, often wedge-shaped crystals that almost always form knee twins as well as penetrating twins according to { 1 12}. Often they are clearly streaked parallel to the b-axis, which can be seen particularly clearly on {210}. In addition to the pinacoid {100}, which determines the habitus and costume , the prisms {201}, {210} and {103} as well as the pinacoid {010} were attached to the crystals with a maximum size of 0.5 × 0.2 × 0.05 mm. detected. Occasionally the crystals come together to form aggregates .

physical and chemical properties

The crystals of Giniit are blackish green to blackish brown, but their line color is always olive green. The surfaces of the opaque, only edge-translucent crystals have a glass-like to grease-like, sometimes also diamond-like sheen , which agrees well with the values ​​for the refraction of light . Medium to high values ​​for light refraction (n α  = 1.775; n β  = 1.803; n γ  = 1.812) and a high value for birefringence (δ = 0.037) were found on the crystals of Giniit . Giniit has a strong pleochroism from X = light brown to Y = dark brown to Z = dark blue-green.

No cleavage was found on the ginnite . Due to its brittleness , it breaks like quartz , with the fracture surfaces being scalloped to half-scalloped. With a Mohs hardness of 3 to 4, the mineral is one of the medium-hard minerals and, like the reference minerals calcite (hardness 3), can be scratched with a copper coin or fluorite (hardness 4) with a pocket knife. The measured density for Giniit is 3.415 g / cm³, the calculated density is 3.41 g / cm³. Giniit is neither in the long term nor in the short wavelength UV light , a fluorescent .

Giniit is difficult to dissolve in hot nitric acid (HNO 3 ) and hot hydrochloric acid (HCl).

Education and Locations

As a very rare mineral formation, Giniit could so far (as of 2018) only be described from three sites. The type locality is the granite pegmatite from Sandamap on the Sandamap North 115 farm near Usakos, constituency of Daures in the Erongo region in Namibia. Giniit was also found in the “ Morassina ” mine near Schmiedefeld and in the “Jeremias Glück” mine ( fairy grottoes ) near Garnsdorf not far from Saalfeld , both in the Saalfeld-Rudolstadt district in the Thuringian Forest , Thuringia , Germany . Both pits are now operated as show mines . Occurrences of Giniit in Austria or Switzerland are therefore not known.

Giniite is a typical secondary mineral due to its type locality , which has formed in the oxidation zone of a granite pegmatite with primary phosphate mineral paragenesis . Both iron and phosphorus come from the weathering of triphylene and barbosalite . In the Thuringian mines it forms locally when the crusts and stalactites are altered on the surfaces of solidified gels. In the "Sandamap pegmatite" the mineral was first found on a par with corroded triphylene and barbosalite. Paragenesis minerals are Hureaulith , Tavorit , Leukophosphit , Whitlockit and Monetit and Phosphosiderit and Mélonjosephit . The succession (age sequence) is indicated with triphylene → hureaulite → dark green, scaly mineral + giniite → tavorite → leukophosphite.

In the Thuringian mines, Giniit u. a. accompanied by the crystallized form of the Diadochite , the Destinecite .

use

Due to its rarity, naturally formed giniite is only of interest to the mineral collector.

Giniit's synthetic analog is a promising material for capturing phosphopeptides from complex tryptic digests, photocatalysts and cathodes for lithium batteries . In all of these applications, crystal morphology is extremely important.

Iron hydroxyl phosphates (Fe x (PO 4 ) y (OH) z · nH 2 O) such as Giniit, Barbosalith, Whitmoreit and Beraunit are important oxidative catalysts for dehydrogenation . They are also significant in the passivation of metal surfaces, corrosion inhibition and in the reactions of iron components with phosphate fertilizers in various soils. Controlling the morphology of micro- and nano-sized Fe x (PO 4 ) y (OH) z · nH 2 O of well-defined form is important for their application in catalysis, the glass industry, and environmental science and technology.

See also

literature

  • Paul Keller: Giniite, Fe 2+ Fe 4 3+ [(H 2 O) 2 | (OH) 2 | (PO 4 ) 4 ], a new mineral from the pegmatite of Sandamab [sic!] Near Usakos, Namibia . In: New yearbook for mineralogy, monthly books . tape 1980 , no. 2 , 1980, p. 49-56 .
  • Paul Keller: Giniit, Fe 2+ Fe 4 3+ [(H 2 O) 2 | (OH) 2 | (PO 4 ) 4 ]: new crystallographic data . In: New yearbook for mineralogy, monthly books . tape 1980 , no. 12 , 1980, pp. 561-563 .
  • Giniite . 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; 64 kB ; accessed on August 11, 2018]).

Web links

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB)
  2. ↑ a b c d e f g h i j k Mindat - Giniite (English)
  3. ↑ a b c d e f Paul Keller: Giniit, Fe 2+ Fe 4 3+ [(H 2 O) 2 | (OH) 2 | (PO 4 ) 4 ]: new crystallographic data . In: New yearbook for mineralogy, monthly books . tape 1980 , no. 12 , 1980, pp. 561-563 .
  4. ^ 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.  495 .
  5. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak Paul Keller: Giniit, Fe 2+ Fe 4 3+ [(H 2 O) 2 | (OH) 2 | (PO 4 ) 4 ], a new mineral from the pegmatite of Sandamab [sic!] Near Usakos, Namibia . In: New yearbook for mineralogy, monthly books . tape 1980 , no. 2 , 1980, p. 49-56 .
  6. ↑ a b Typmineral catalog Germany - storage of the type material for Giniit
  7. ↑ a b c Giniite . 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; 64  kB ; accessed on August 11, 2018]).
  8. ↑ DR Corbin, JF Whitney, WC Fultz, GD Stucky, MM Eddy, AK Cheetham: CSynthesis of open-framework transition-metal phosphates using organometallic precursors in acidic media. Preparation and structural characterization of Fe 5 P 4 O 20 H 10 and NaFe 3 P 3 O 12 . In: Inorganic Chemistry . tape 25 , no. 14 , 1986, pp. 2279-2280 , doi : 10.1021 / ic00234a001 .
  9. ↑ Mindat - Number of localities for Giniit
  10. ↑ a b List of locations for Giniit in the Mineralienatlas and Mindat
  11. ↑ Bernd Ullrich, K.-U. Hantsch, K. Müller, Heiner Siedel, B. Ullrich: Secondary mineral formations in the alum slate mine "Morassina" near Schmiedefeld on Rennweg (Saalfelder Höhe) in the Thuringian Slate Mountains . In: Contributions to the geology of Thuringia New series . tape 12 , 2005, p. 41-69 .
  12. ↑ B. Ullrich, B. Ullrich: Schwertmannite in the weathering products of the alum slate mine "Morrasina" near Schmiedefeld in the Thuringian Slate Mountains . In: The opening . tape 61 , no. 2 , 2010, p. 75-79 .
  13. ↑ a b c d Bernd Ullrich: On the mineralogy of anthropogenically induced alteration processes - secondary minerals of the historical alum slate mining of Saalfeld and Schmiedefeld in the Thuringian slate mountains . In: Geologica Saxonica . tape 64 , 2018, p. 67–79 ( senckenberg.de [PDF; 5.6 MB ; accessed on August 9, 2018]).
  14. ↑ Renato Gonçalves, Ricardo Martins, Carlos M. Costa, Stanislav Ferdov, Senentxu Lanceros-Méndez: Crystal morphology control of synthetic giniite by alkaline cations and pH variations . In: Crystal Growth & Design . tape 17 , no. 9 , 2017, p. 4710-4714 , doi : 10.1021 / acs.cgd.7b00590 .
  15. ↑ Qun Chen, Chengzhen Wei, Yizhou Zhang, Huan Pang, Qingyi Lu, Feng Gao: Single-crystalline hyperbranched nanostructure of Iron Hydroxyl Phosphate Fe 5 (PO 4 ) 4 (OH) 3 2H 2 O for highly selective capture of phosphopeptides . In: Scientific Reports . tape 4 , Article number 3753, 2014, doi : 10.1038 / srep03753 , PMC 3894561 (free full text).