Eyselit

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Eyselit
General and classification
other names

IMA 2003-052

chemical formula Fe 3+ Ge 4+ 3 O 7 (OH)
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DM.20 ( 8th edition : IV / F.17)
07.03.03.01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol unknown
Space group unknown
Lattice parameters a  = 8.302  Å ; b  = 9.718 Å; c  = 4.527 Å
Formula units Z  = 2
Frequent crystal faces {100}, {010}, {011}, {001}
Physical Properties
Mohs hardness "Soft" (1 to 2)
Density (g / cm 3 ) 3,639 (calculated)
Cleavage no
Break ; Tenacity brittle; uneven
colour dirty brown-yellow (aggregates) to yellowish-light brown (crystals)
Line color brownish yellow
transparency opaque (aggregates) to transparent (crystals)
shine Glass gloss
Crystal optics
Refractive indices n α  > 1.8
n γ  > 1.8
Birefringence δ = "low"
Optical character biaxial positive
Axis angle 2V = "large"

Eyselite is a very rare mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical formula Fe 3+ Ge 4+ 3 O 7 (OH), so it is chemically an iron - germanium oxide with additional hydroxide ions .

Eyselit forms aggregates that appear macroscopically xenomorphic and consist of randomly oriented subidiomorphic to idiomorphic , platy to very thin prismatic, elongated according to [001] crystals up to a maximum of 20 µm in length. The crystals sit together with tennantite in a cavity in renierite-germanite ore. The mineral was only found as a single specimen in the Tsumeb Mine , Namibia.

Etymology and history

The only known specimen, Eyselite, was acquired in 1977 by Terry Maxwell Seward from a collection of altered germanium-containing ores owned by Sid Pieters of Windhoek , Namibia. The secondary mineral sitting on the step was analyzed by powder diffractometry in the early 1990s, but remained unidentified. Only further investigations at the end of 2002 showed that it was a new phase, recognized in 2003 under the number "IMA 2003-052" by the International Mineralogical Association (IMA) and in 2004 by a Canadian-Swiss-US research team with Andrew C. Roberts from the Geological Survey of Canada , Ottawa , Terry M. Seward and Eric Reusser from the Eidgenössische Technische Hochschule Zürich , Graham JC Carpenter from the Materials Technology Laboratories (CANMET) in Ottawa, Joel D. Grice from the Canadian Museum of Nature in Ottawa and Simon M. Clark and Matthew A. Marcus of the Lawrence Berkeley National Lab in Berkeley , was described in the science magazine "The Canadian Mineralogist" as Eyselite.

The mineral was named after the German professor for crystallography Walter Hans Eysel (1935–1999) at the Ruprecht-Karls-Universität , Heidelberg , in recognition of his work on the Germanates and for his numerous contributions to the Powder Diffraction File of the International Center for Diffraction Data (ICDD).

The type material is listed in the “Systematic Reference Series” of the “National Mineral Collection” in the Geological Survey of Canada, Ottawa, under the collection no. 68093 kept.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Eyselit belonged to the class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates (water-containing oxides with a layer structure)", where it was named after the " Stottit Group "with the system no. IV / F.17 and the other members jeanbandyite , mopungite , stottite and tetrawickmanite .

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 the Eyselit to the class of "oxides and hydroxides" and there in the department of "metal: oxygen = 1: 2 and comparable" a. However, this department is further subdivided according to the size of the cations involved and the crystal structure, so that the mineral is classified in the subdivision “M. With large (± medium-sized) cations; unclassified ”is to be found, where it forms the unnamed group 4.DM.20 as the sole representative .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also sorts the Eyselite into the class of oxides, but there into the division of “multiple oxides”. Here he is the only member of the unnamed group 07.03.03 within the subdivision of “ Multiple oxides with 2+ and higher charged cations ”.

Chemism

Mean values ​​from nine microprobe analyzes on Eyselit from Tsumeb led to contents of 0.06% CaO; 18.54% Fe 2 O 3 ; 1.01% Ga 2 O 3 ; 77.75% GeO 2 and [2.64]% H 2 O (calculated). On the basis of 8 oxygen atoms per formula unit, the empirical formula was calculated from this (Fe 3+ 0.93 Ga 3+ 0.04 ) Σ = 0.97 Ge 4+ 2.98 O 6.90 (OH) 1.17 , which was idealized to Fe 3+ Ge 4+ 3 O 7 (OH), which requires levels of 19.83% Fe 2 O 3 , 77.93% GeO 2 and 2.24% H 2 O.

The only two other natural Fe-Ge-Oxi components are brunogeierite (Ge 2+ , Fe 2+ ) Fe 3+ 2 O 4 and stottite Fe 2+ Ge 4+ (OH) 6 .

Crystal structure

Eyselite crystallizes orthorhombically with the lattice parameters a  = 8.302  Å ; b  = 9.718  Å and c  = 4.527 Å as well as two formula units per unit cell . The crystal class and space group cannot be determined due to the size of the crystals, the growth phenomena on the crystal faces and the partially hollow crystals. The X-ray powder data are singular and show no similarities with those of another germanate, silicate or any other inorganic phase listed in the powder diffraction file.

Using micro-X-ray atomic absorption spectroscopy, it was possible to show that all iron in the eyselite is trivalent, that the germanium atoms are octahedral coordinated and that the structure of the mineral is very likely to be in good order.

properties

morphology

Eyselit forms macroscopically xenomorphic aggregates from randomly oriented subidiomorphic to rarely also idiomorphic, platy to very thin prismatic, [001] elongated crystals up to a maximum of 20 µm in length. The length-to-width ratio of the crystals, which are typically 20 µm × 14 µm × 1 µm in size, is approximately 3: 1. The main shape that determines the costume is the pinacoid {100}. Then there are the very thin pinacoid {010}, the rounded prism {011} and the very thin, also rounded basic pinacoid {001}. The z. Sometimes hollow crystals often show pronounced step growth on the surfaces of {100}. The tiny eyselite crystals sit in the 4–5 mm large cavity in the primary ore loosely on the sulphide minerals lining the cavity.

physical and chemical properties

The aggregates and crystals of the eyselite vary in color from dirty brown-yellow (in aggregates) to yellowish-light brown (crystals). Their line color , on the other hand, is always brownish-yellow. The surfaces of the opaque (aggregates) to transparent (crystals) Eyselite individuals show a glass-like sheen . In transmitted light (thin section), Eyselit is light pale yellow with very high refraction and low birefringence.

Eyselite has no observable cleavage properties , but due to its brittleness it breaks like triphyline or amblygonite , with the fracture surfaces being uneven. It is described as "soft", so with a Mohs hardness of 1 to 2 it belongs to the soft minerals that, like the reference minerals talc (hardness 1), can be scraped with the fingernail or plaster of paris (hardness 2) scratched with the fingernail. Measured values ​​for the density of the Eyselite do not exist, the calculated density for the mineral is 3.639 g / cm³.

Education and Locations

Eyselite occurs as a typical secondary formation in the corroded ore of a complex Cu-Pb-Zn deposit in carbonate rocks. Iron and germanium come from the decomposition of primary germanium ores and sulfidic ore minerals such as germanite , renierite and tennantite . The mineral formed in the alteration of the germanium-containing sulfide minerals by aqueous, through the ore body migrating solutions (groundwater). No other secondary minerals were observed in direct association with Eyselit .

As an extremely rare mineral formation, Eyselite could only be described from one source so far (as of 2016). The type locality of the mineral is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto Region , Namibia . The exact location within the "Tsumeb Mine" is not known.

use

Due to its rarity, Eyselite is only of interest to mineral collectors.

See also

literature

  • Andrew C. Roberts, Terry M. Seward, Eric Reusser, Graham JC Carpenter, Joel D. Grice, Simon M. Clark, Matthew A. Marcus: Eyselite, Fe 3+ Ge 4+ 3 O 7 (OH), a new mineral species from Tsumeb, Namibia . In: The Canadian Mineralogist . tape 42 , 2004, p. 1771–1776 , doi : 10.2113 / gscanmin.42.6.1771 ( rruff.info [PDF; 543 kB ]).

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q Andrew C. Roberts, Terry M. Seward, Eric Reusser, Graham JC Carpenter, Joel D. Grice, Simon M. Clark, Matthew A. Marcus: Eyselite, Fe 3+ Ge 4+ 3 O 7 (OH), a new mineral species from Tsumeb, Namibia . In: The Canadian Mineralogist . tape 42 , 2004, p. 1771–1776 , doi : 10.2113 / gscanmin.42.6.1771 ( rruff.info [PDF; 543 kB ]).
  2. ↑ Mineralienatlas - Mineral description Eyselit
  3. ↑ Mindat - Number of localities for Eyselit
  4. ↑ a b List of localities for Eyselite in the Mineralienatlas and Mindat