Rappoldite

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Rappoldite
Rappoldite-779740.jpg
Aggregate of reddish-brown rappoldite crystals on quartz
from the type locality Grube Rappold (field of view 5 mm)
General and classification
other names

IMA 1998-015

chemical formula
  • Pb (Co, Ni) 2 (AsO 4 ) 2 · 2H 2 O
  • Pb (Co, Ni) 2 [H 2 O | AsO 4 ] 2
  • PbCo 2 (AsO 4 ) 2 • 2H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.CG.20 ( 8th edition : VII / C.31)
02/40/09/05
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 11.190  Å ; b  = 10.548 Å; c  = 7.593 Å
α  = 100.38 °; β  = 109.59 °; γ  = 98.96 °
Formula units Z  = 4
Frequent crystal faces {210}, {001}
Twinning without exception twinned, with {2 3 0} as the twin level
Physical Properties
Mohs hardness 4.5
Density (g / cm 3 ) 5.28 (calculated)
Cleavage no
Break ; Tenacity clamshell; brittle
colour red to red-brown
Line color light yellow brown
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.85 (calculated)
n β  = 1.87
n γ  = 1.90
Birefringence δ = 0.05
Optical character biaxial positive
Axis angle 2V = 85 ° (measured); 2V = 80 ° (calculated)
Pleochroism none
Other properties
Chemical behavior Completely soluble in warm dilute HCl

Rappoldite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the triclinic crystal system with the chemical composition Pb (Co, Ni) 2 (AsO 4 ) 2 · 2H 2 O and is therefore chemically a water-containing lead - cobalt - nickel - arsenate .

Rappoldit develops prismatic or tabular crystals up to 1 mm long and 0.3 mm in diameter, which come together to form small, rosette-shaped or spherical aggregates . The mineral is found together with cobalt austinite on weathered erythrin and sits with its accompanying minerals in drusen in the granular, cellular quartz vein . The type locality of the mineral is the Rappold treasure trove in the Schneeberg district of Neustädtel - a formerly independent mountain town in the Saxon Ore Mountains .

Etymology and history

The discoverer of Rappoldite is the Schneeberg collector Lutz Schlegel , who found the mineral in 1991 during earthworks in Schneeberg-Neustädtel, during which parts of the heap of the Rappold treasure trove and the heap material used in road construction work were uncovered. After initial determinations, the mineral was identified as tsumcorite. Subsequent investigations then led to the result that it is not tsumcorite, but a previously unknown type of mineral from the tsumcorite group, which was introduced in 1998 as the "unnamed Pb-Co-Ni-As mineral". After further detailed mineralogical, chemical and structural work, the mineral was recognized in 1998 by the International Mineralogical Association (IMA) under the number "IMA 1998-015" and in 2000 by an Austrian-German research team with Herta Silvia Effenberger , Werner Krause , Heinz -Jürgen Bernhardt and Mirko Martin described in the English science magazine "Mineralogical Magazine" as Rappoldite.

The mineral was named after its place of discovery, the "Fundgrube Rappold" in Schneeberg-Neustädtel, which got its name after the mining entrepreneur Friedrich Rappolt (Rappold) who died between 1513 and 1516. Between 1475 and 1494 Rappolt founded the mine named after him in Schneeberg-Neustädtel, which in 1503/04 was the largest Schneeberg silver mine, a. a. reached a technical peak with the first walling of the pit. The hut house and cutting bench have been preserved from the pit and are now protected as a technical monument .

Type material of the mineral (holotype) is kept in the geoscientific collections of the Technical University Bergakademie Freiberg in Germany (catalog no. 79924 at location c 8.7).

classification

The current classification of the International Mineralogical Association (IMA) counts rappoldite to the tsumcorite group with the general formula Me (1) Me (2) 2 (XO 4 ) 2 (OH, H 2 O) 2 , in which Me (1), Me (2) and X different positions in the structure of the minerals of the tsumcorite group with Me (1) = Pb 2+ , Ca 2+ , Na + , K + and Bi 3+ ; Me (2) = Fe 3+ , Mn 3+ , Cu 2+ , Zn 2+ , Co 2+ , Ni 2+ , Mg 2+ and Al 3+ and X = As 5+ , P 5+ , V 5+ and represent S 6+ . To Tsumcoritgruppe include not only Rappoldit still Cabalzarit , Cobaltlotharmeyerit , Cobalttsumcorit , Ferrilotharmeyerit , Gartrellit , Helmutwinklerit , Kaliochalcit , Krettnichit , Lotharmeyerit , Lukrahnit , Manganlotharmeyerit , Mawbyit , Mounanait , Natrochalcit , Nickellotharmeyerit , Nickelschneebergit , Nickeltsumcorit , Phosphogartrellit , Schneebergit , Thometzekit , Tsumcorit , Yancowinnait and Zinc Gartrellite .

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Rappoldit belonged to the mineral class of "phosphates, arsenates and vanadates" and then to the Department of "water containing phosphates without foreign anions " where he along with Cabalzarit , Cobaltlotharmeyerit , Cobalttsumcorit , Ferrilotharmeyerit , Gartrellit , Helmutwinklerit , Krettnichit , Lotharmeyerit , Lukrahnit , Manganlotharmeyerit , Mawbyit , Mounanait , Nickellotharmeyerit , Nickelschneebergit , Phosphogartrellit , Schneebergit , Thometzekit , Tsumcorit and Zinkgartrellit the "Tsumcorit-Gartrellit group" with the system number. VII / C.31 formed.

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also assigns Rappoldite to the category of “phosphates etc. without additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of phosphate, arsenate or vanadate complex to the water of crystallization content , so that the mineral can be classified according to its composition in the subsection “With large and medium-sized cations; RO 4  : H 2 O = 1: 1 "is to be found, where together with the other members gartrellite , helmutwinklerite , lukrahnite , phosphogartrellite and zinc gartrellite the" Helmutwinklerite group "with the system no. 8.CG.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns rappoldite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here it is together with cobalt sumcorite, helmutwinklerite, mawbyite, nickel schneebergite, snow mountainite, Thometzekit and tsumcorite in the " helmutwinklerite subgroup " with the system no. 02/40/09 within the subsection “Phosphates containing water, etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O)”.

Chemism

Eleven microprobe analyzes on Rappoldit yielded mean values ​​of 35.27% PbO; 0.12% CaO; 0.11% Bi 2 O 3 ; 0.28% Fe 2 O 3 ; <0.05% Al 2 O 3 ; 4.52% ZnO; <0.05% CuO; 11.60% CoO, 7.31% NiO, 35.82% As 2 O 5 ; 0.11% SO 3 and 5.62% H 2 O (theoretical content). From this, the empirical formula (Pb 1.01 Ca 0.01 ) Σ = 1.02 (Co 0.99 Ni 0.62 Zn 0.35 Fe 2+ 0.02 ) Σ = 1 was calculated on the basis of 10 oxygen atoms , 98 [(AsO 4 ) 1.99 (SO 4 ) 0.01 ] Σ = 2.00 [(OH) 0.02 (H 2 O) 1.98 ] Σ = 2.00 , corresponding to Pb (Co , Ni) 2 (AsO 4 ) 2 · 2H 2 O has been simplified.

Rappoldite is a representative of the tsumcorite group . The general formula for the tsumcorite group is Me (1) Me (2) 2 (XO 4 ) 2 (OH, H 2 O) 2 with Me (1) = Pb, Ca, Na and Bi; Me (2) = Fe, Mn, Cu, Zn, Co, Ni and Al as well as X = P, As, V and S. Mixed crystal formation occurs mainly on the Me (2) position, but less frequently on the X and Me positions (1) position instead.

Since there are only divalent cations on the Me (2) positions in Rappoldite and substitution with hydroxyl groups is therefore not necessary, the mineral contains exactly two water molecules (H 2 O).

Rappoldite is the Co 2+ -dominant analogue of the Zn 2+ -dominated helmutwinklerite.

Crystal structure

Rappoldite crystallizes in the triclinic crystal system in the space group P 1 (space group no. 2) with the lattice parameters a  = 11.190  Å ; b  = 10.548 Å; c  = 7.593 Å; α = 100.38 °; β = 109.59 ° and γ = 98.96 ° as well as four formula units per unit cell . Template: room group / 2

The crystal structure of rappoldite consists of coordination polyhedra , which are linked by common edges to form chains parallel [010]. AsO 4 - tetrahedra with common corners connect these chains, creating layers lying parallel to the ab surface. The layers are connected by hydrogen bonds and by Pb [6 + 2] atoms at the Me (1) position, which occupy specific positions with symmetry 1 between these layers. The Me (2) position is split as in the other representatives of the triclinic Tsumcoritgruppe in two different positions. In the triclinic subcell of rappoldite, half of the two Me (2) positions are safely occupied by cobalt atoms; Nickel and zinc atoms are the other main components in these positions, Fe 3+ only plays a subordinate role. During the refinement, the occupancy of the two positions Me (2a) and Me (2b) in rappoldite was fixed to the analytically determined values ​​for Ni and Fe. For the Co: Zn ratio, on the other hand, a separate variation was allowed for the two positions with the simultaneous assumption of full occupancy. The refined ratio is practically identical on both Me positions. Due to the similarity of the geometry of the refined cast and the distance parameter of the Me (2a) O 6 - and Me (2b) O 6 - polyhedron no indications exist on an ordering on these positions.

The minerals of the tsumcorite group can be divided into three different subgroups (tsumcorite, helmutwinklerite and gartrellite subgroup), which are characterized by different structural types. Rappoldite belongs to the representatives of the Helmutwinklerite subgroup with the general formula Me (1) 2+ Me (2) 2+ 2 ( X 5+ O 4 ) 2 · 2H 2 O, for which an almost complete solid solution formation on the Me (2 ) Position with Me 2+ (Co, Ni, Zn) ↔ Cu 2+ is assumed. Due to the requirement of four hydrogen bonds per formula unit, these minerals all have triclinic symmetry. The unit cell is enlarged compared to the representatives of the tsumcorite subgroup and contains four formula units. This is caused by a partial ordering of the hydrogen bonds, which avoids symmetry-restricted hydrogen bonds.

Rappoldite is isotypic (isostructural) to helmutwinklerite and possibly also to pure formula Thometzekit, but not to monoclinic sulfate-containing Thometzekit.

properties

Costume and habitus of Rappoldit
Rappoldit 1.png
according to {001} tabular crystal, normal setup
Rappoldit 2.png
same crystal, tilted from the normal setup

morphology

Rappoldit develops red and idiomorphic, parallel [ 1 20] prismatic or tabular crystals up to 1 mm long and 0.3 mm in diameter, which come together to form small, rosette-shaped or spherical aggregates . There are also red-brown aggregates of tabular crystals that form adhesions with small amounts of cobalt solder armyerite . Spherical units are also described. The shapes that determine the costume are the pinacoid parallel to the c-axis {210} and the third pinacoid {001}. Since these two planar shapes alone do not define a closed crystal shape, the pinacoid {2 1 0} was used for the crystal drawings on the left to complete the crystals .

All examined rappoldite crystals are without exception twinned , with {2 3 0} forming the twin plane.

physical and chemical properties

The crystals of Rappoldite are red to red-brown, its line color is indicated as light yellow-brown. The surfaces of the transparent crystals have a glass-like sheen , which is also in agreement with the values ​​for the refraction of light (n x  = 1.85, n z  = 1.90).

The mineral shows no cleavage , but due to its brittleness it breaks like quartz , whereby the fracture surfaces are shell-shaped. With a Mohs hardness of 4.5, rappoldite is one of the medium-hard minerals, so it stands between the reference minerals fluorite (hardness 4) and apatite (hardness 5) and, like these, can be easily scratched with a pocket knife. The density of the mineral could not be measured, its calculated density is 5.28 g / cm³.

Rappoldit is completely soluble in warm dilute hydrochloric acid (HCl).

Education and Locations

Light reddish brown rappoldite from the Rappold pit (field of view 3 mm)

Rappoldite is a typical secondary mineral , which was formed through weathering of primary ore minerals in the oxidation zone of an arsenic-containing hydrothermal bismuth-cobalt-nickel-silver deposit . It emerged from the decomposition of lead, cobalt, nickel and zinc-containing ore minerals such as galena , representatives of the skutterudite - nickel cutterudite - mixed crystal series and sphalerite , the arsenic originating from the decomposition of arsenides (skutterudite).

On the type level, the rappoldite sits in cellular quartz. Other secondary minerals found in the heap are cobalt solder armyerite, cobalt austinite, scorodite, bariopharmacosiderite, olivite, conichalcite, erythrin, arseniosiderite, mimetite and beudantite, as well as the primary ore minerals, solid silver , solid bismuth , acanthite , galenudite, pyrite and pyrite . As directly Rappoldit associated it occur among others Cobaltaustinit and Cobaltlotharmeyerit.

As a very rare mineral formation, Rappoldite could so far (as of 2017) only be described by its type locality . The type locality is the “Fundgrube Rappold” near Schneeberg on the edge of the Schneeberg-Neustädtel cobalt field, Erzgebirgskreis , western Ore Mountains , Saxony , Germany . Locations for Rappoldite in Austria and Switzerland are therefore unknown.

use

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

See also

literature

  • Herta Effenberger, Werner Krause, Heinz-Jürgen Bernhardt, Mirko Martin: On the symmetry of tsumcorite group minerals based on the new species rappoldite and zincgartrellite . In: Mineralogical Magazine . tape 64 , no. 6 , 2000, pp. 1109–1126 , doi : 10.1180 / 002646100549922 ( rruff.info [PDF; 1.1 MB ]).

Web links

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

Individual evidence

  1. ↑ 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 Herta Effenberger, Werner Krause, Heinz-Jürgen Bernhardt, Mirko Martin: On the symmetry of tsumcorite group minerals based on the new species rappoldite and zincgartrellite . In: Mineralogical Magazine . tape 64 , no. 6 , 2000, pp. 1109–1126 , doi : 10.1180 / 002646100549922 ( rruff.info [PDF; 1.1 MB ]).
  2. ^ 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.  730 .
  3. ↑ a b c Mindat - Rappoldite
  4. ↑ a b c d e Mirko Martin, Fritz Schlegel: Kobaltaustinit and Tsumcorit from the Rappold treasure trove in Schneeberg / Saxony . In: Lapis . tape 17 , no. 10 , 1992, pp. 28-29 .
  5. ↑ a b c d Werner Krause, Klaus Belendorff, Heinz-Jürgen Bernhardt, Catherine McCammon, Herta Effenberger, Werner Mikenda: Crystal chemistry of the tsumcorite-group minerals. New data on ferrilotharmeyerite, tsumcorite, thometzekite, mounanaite, helmutwinklerite, and a redefinition of gartrellite . In: European Journal of Mineralogy . tape 10 , 1998, pp. 179-206 , doi : 10.1127 / ejm / 10/2/0179 .
  6. ↑ Saxon Biography - Friedrich Rappolt
  7. ↑ Type mineral catalog Germany - storage of the holotype stage Rappoldite
  8. ↑ Catalog of Type Mineral Specimens - R. (PDF 67 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
  9. ↑ Peter Süsse, Günther Schnorrer: Helmutwinklerite, a new arsenate mineral from Tsumeb, SW Africa . In: New yearbook for mineralogy, monthly books . tape 1980 , no. 3 , 1980, p. 118-124 .
  10. ^ Karl Schmetzer, Bernhard Nuber, Olaf Medenbach: Thometzekite, a new mineral from Tsumeb, Namibia, and symmetry relations in the tsumcorite-helmutwinklerite family . In: New yearbook for mineralogy, monthly books . tape 1985 , no. 10 , 1985, pp. 446-452 .
  11. ↑ Mineral Atlas: Rappoldite
  12. ↑ Mindat - Number of localities for Rappoldite
  13. ↑ Find location list for rappoldite at the Mineralienatlas and at Mindat