Vonbezingit

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Vonbezingit
General and classification
chemical formula Ca 6 Cu 3 [(OH) 12 | (SO 4 ) 3 ] • 2H 2 O
Mineral class
(and possibly department) 		Sulphates (selenates, tellurates, chromates, molybdates and tungstates)
System no. to Strunz
and to Dana 		7.DD.65 ( 8th edition : VI / D.18)
05/31/01/01
Similar minerals Azurite
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = 15.122  Å ; b  = 14.358 Å; c  = 22.063 Å
β  = 108.68 °
Formula units Z  = 8
Frequent crystal faces {110}, {010}, {100}, {111} and {101}
Twinning merohedral twins according to {001}
Physical Properties
Mohs hardness ≈ 4
Density (g / cm 3 ) 2.82 (measured), 2.81 (calculated)
Cleavage no cleavage and no divisibility observed
Break ; Tenacity imperfectly scalloped; brittle
colour deep azure
Line color Light Blue
transparency semi-transparent (semi-transparent)
shine Semi-glass gloss (crystal surfaces), glass gloss (fracture surfaces)
Crystal optics
Refractive indices n α  = 1.590
n β  = 1.610
n γ  = 1.619
Birefringence δ = 0.029
Optical character biaxial negative
Axis angle 2V = 65 ° (measured), 2V = 67 ° (calculated)
Pleochroism strong from n γ  = dark blue via n β  = gray blue to n α  = light blue.

Vonbezingit is an extremely rarely occurring mineral from the mineral class of " sulfates " (and relatives, see classification). It crystallizes in the monoclinic crystal system with the chemical composition Ca 6 Cu 3 [(OH) 12 | (SO 4 ) 3 ] · 2H 2 O and is therefore chemically a water-containing calcium - copper - sulfate with additional hydroxide ions .

Vonbezingit develops idiomorphic, parallel [001] elongated crystals up to 5 cm in length, which are deeply dark blue in color and are extremely similar to the basic copper carbonate azurite in terms of color and morphology . They can come together to form aggregates of smaller crystals that have grown in parallel and reach a maximum size of 3 cm.

Etymology and history

During the investigation of minerals from the Kalahari manganese ore fields in the north-western province of Northern Cape , Republic of South Africa , a striking blue mineral from the “Wessels Mine” was discovered in 1986, which showed clear similarities to azurite, but because of the associated minerals could not be azurite. The Austrian-South African hobby mineralogist Karl-Ludwig von Bezing presented this mineral, which he could not identify , to Roger Dixon , who was then curator of the Museum of the Geological Service of South Africa , who recognized it as a new mineral.

Although samples of this new mineral were sent to the American Museum of Natural History in New York, there was no exact identification of the phase from the "Wessels Mine" due to lack of time, so that in the updates on the mineralogy of the Kalahari manganese ore fields only from an unidentified " azure-blue copper sulfate " was mentioned. Only after further intensive investigations and extensive analyzes by a US team led by the mineralogists Yongshan Dai and George E. Harlow was the species presented to the International Mineralogical Association (IMA), which recognized it as a new mineral in 1991. It was first described as Vonbezingit in 2012 by Dai and Harlow in the American science magazine "The American Mineralogist". The authors named the mineral after its finder, the Austrian-South African doctor, radiologist and hobby mineralogist Ludi von Bezing (* 1945) in recognition of his contributions to the mineralogy of the Kalahari manganese ore fields.

The type material for Vonbezingit is stored under catalog number T100748 in the collection of the American Museum of Natural History in New York City , New York State in the USA .

classification

Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Vonbezingite belonged to the mineral class of "sulfates (including selenates , tellurates , chromates , molybdates and tungstates )" and there to the department of "anhydrous sulfates, with foreign anions " where, together with kainite , natrochalcite and uklonscovite, the kainite-natrochalcite group with the system no. VI / D.18 .

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 classifies Vonbezingite in the category of "sulfates (selenates, etc.) with additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral is classified in the sub-section “With only medium-sized cations; Layers of edge-sharing octahedra ” can be found, where it is the only member of the unnamed group 7.DD.65 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Vonbezingite to the class of “sulfates, chromates and molybdates” and there to the “hydrous sulfates with hydroxyl or halogen” class. Here he is the only member of the unnamed group May 31, 2001 within the subdivision of “ Hydrous sulfates with hydroxyl or halogen with (A + B 2+ ) 3 (XO 4 ) Z q × x (H 2 O) ”.

Chemism

Six microprobe analyzes and thermogravimetric analyzes on Vonbezingit resulted in mean values ​​of 35.4% CaO; 25.5% CuO; 24.0% SO 3 and 15.6% H 2 O. Based on 26 oxygen atoms, the empirical formula Ca 6.03 Cu 3.07 (SO 4 ) 2.87 (OH) 12.46 is calculated from them . 2.06H 2 O, which was idealized to Ca 6 Cu 3 (SO 4 ) 3 (OH) 12 · 2H 2 O. This requires contents of 35.07% CaO, 24.87% CuO, 25.04% SO 3 and 15.02% H 2 O. Small deficits in SO 3 (less than 1.1%) can be due to minor substitution of boron or carbon can be recycled for sulfur .

Chemically similar are devillin , Cu 4 Ca [(OH) 6 | (SO 4 ) 2 ] · 3H 2 O, as well as serpierite and orthopserpierite , both Ca (Cu, Zn) 4 [(OH) 6 | (SO 4 ) 2 ] · 3H 2 O.

Crystal structure

Vonbezingit crystallizes in the monoclinic crystal system in the space group P 2 1 / c (space group no. 14) with the lattice parameters a = 15.122  Å ; b = 14.358 Å; c = 22.063 Å and β = 108.68 ° as well as eight formula units per unit cell . Template: room group / 14

The structure of the Vonbeckite contains an asymmetric unit with 76 non- hydrogen positions. The copper atoms are in six different positions and all show a distortion of the coordination polyhedron, which is due to the Jahn-Teller effect . In the structure, [7] Ca polyhedra with common edges form chains parallel [010], which are connected by further [7] Ca polyhedra to form layers of rings of three and six parallel (001). A plane containing Cu (OH) 4 (SO 4 ) 2 groups is sandwiched between these layers , these groups being linked to one another by hydrogen bonds . The thick, heteropolyhedral plates alternate with the planes containing the Cu (OH) 4 (SO 4 ) 2 groups.

Alternatively, Vonbezingit can also be viewed as a structure with zigzag and planar polyhedron layers parallel (001). There are four polyhedral zigzag layers of symmetrically equivalent Ca positions at z ≈  1 ⁄ 8 , 3 ⁄ 8 , 5 ⁄ 8 and 7 ⁄ 8 , two zigzag layers of equivalent Cu1 x and S1 x at z ≈ 0 and 1 ⁄ 2 as well as two nearly planar layers of equivalent Cu2 x and S2 x polyhedra at z ≈  1 ⁄ 4 and 3 ⁄ 4 .

Vonbezingit has a on a C 2 / c -Pseudozelle (b is halved) based super structure of disordered S2O 4 - tetrahedra , which probably have a high temperature polymorph of Ca 6 Cu 3 [(OH) 12 | (SO 4 ) 3 ] · 2H 2 represents O. The structure described represents a new type of structure compared to other hydrated Ca-Cu sulfates. Structurally similar minerals are Devillin, Serpierit, Campigliait and Ktenasit . Common to all of these phases is a structure based on layers of octahedrally coordinated cations as in brucite . Template: room group / 15

properties

morphology

At its type locality, Vonbezingit forms idiomorphic crystals up to 5 cm in size, which are almost always more or less stretched along the c-axis [001]. The prism {110} and the pinacoids {010} and {100} are decisive for the costume of natural crystals . {111} and {101} were identified on other surface shapes. In addition, merohedral twins according to {001} have been described. Occasionally the Vonbezingite crystals form aggregates of smaller crystals that are intergrown in parallel and reach a maximum size of 3 cm.

Vonbezingite often contains tiny, micrometer-sized inclusions of azurite and barite .

physical and chemical properties

Vonbezingite crystals are deep azure blue, but their line color is always light blue. The surfaces of the translucent to semi-transparent crystals show a glass-like gloss in accordance with the values ​​for light refraction , while the fracture surfaces have a glass-like gloss.

Vonbezingit has a medium-high refraction (n α  = 1.590, n β  = 1.610, n γ  = 1.619) and a medium-high birefringence (δ = 0.029). In transmitted light, Vonbezingit shows a strong pleochroism from n γ  = dark blue via n β  = gray blue to n α  = light blue. In polarized light, Vonbezingit has anomalous blue interference colors in all non-extinction orientations due to the dark blue color.

In contrast to most of the other sulphate minerals containing water of crystallization, neither cleavage nor divisibility could be observed in the Vonbezingite crystals . Due to its brittleness , however , it breaks like galena , with the fracture surfaces being imperfectly scalloped. The mineral has a Mohs hardness of about 4 and is therefore one of the medium-hard minerals that, like the reference mineral fluorite, can be easily scratched with a knife. Vonbezingit is neither in the long term nor in the short wavelength UV light , a fluorescent .

In terms of color and morphology, azurite is very similar. Vonbezingit can be of azurite but by its matt crystal faces, the lack of cleavage, lower refractive indices, lower density as well as the different chemical composition and the completely different X-ray - diffraction pattern differ.

Education and Locations

The associated minerals and the texture of the Vonbezingite aggregates suggest that Vonbezingite and its accompanying minerals were formed from surface or groundwater during an evaporation period at ambient temperature and atmospheric pressure. The micrometer-sized barite and azurite inclusions, like the associated minerals, suggest that the crystallizing solution was saturated with various oxy salts, of which calcium and sulfate were the most common and important.

Paragenesis minerals from the original find are yellowish Sturmanite in two different generations, bultfonteinite , brucite , Vesuvian , ettringite , gypsum , calcite , barite, azurite and others.

As an extremely rare mineral formation, Vonbezingite has so far (as of 2018) only been detected at one site and, moreover, there only in a single solution cavity, which also only provided around 50 steps. The type locality is block 17 in the “Wessels Mine” near Hotazel not far from Kuruman , Kalahari manganese ore fields, Northern Cape Province , South Africa .

Locations in Germany , Austria and Switzerland are therefore unknown.

use

Due to its rarity, Vonbezingit is an extremely sought-after mineral even among mineral collectors. Beyond that, however, it has no meaning.

See also

literature

  • Yongshan Dai, George E. Harlow: Description and crystal structure of vonbezingite, a new Ca-Cu-SO 4 -H 2 O mineral from the Kalahari manganese field, South Africa . In: The American Mineralogist . tape 77 , no. 11-12 , 1992, pp. 1292-1300 (English).
  • Vonbezingite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 67 kB ; accessed on February 9, 2018]).

Web links

Individual evidence

  1. ^ A b c 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.  405 .
  2. ↑ 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 Yongshan Dai, George E. Harlow: Description and crystal structure of vonbezingite, a new Ca-Cu-SO 4 - H 2 O mineral from the Kalahari manganese field, South Africa . In: The American Mineralogist . tape 77 , no. 11-12 , 1992, pp. 1292–1300 (English, minsocam.org [PDF; 1.1 MB ; accessed on February 10, 2018]).
  3. ^ A b c Bruce Cairncross, Roger Dixon: Minerals of South Africa . 1st edition. Geological Society of South Africa, Johannesburg, Republic of South Africa 1995, ISBN 0-620-19324-7 , pp. 251 (English).
  4. ^ A b Bruce Cairncross: Who's Who in Mineral Names: Karl-Ludwig von Bezing (b. 1945) . In: Rocks & Minerals . tape 87 , no. 5 , 2012, p. 439–441 , doi : 10.1080 / 00357529.2012.709454 (English, researchgate.net [PDF; 754 kB ; accessed on February 10, 2018]).
  5. ^ A b c Bruce Cairncross, Nicolas J. Beukes: The Kalahari Manganese Adventure - the adventure continues . 1st edition. Random House Struik, Capetown, Republic of South Africa 2013, ISBN 978-1-920572-88-4 , pp. 342-344 (English).
  6. ^ A b c Karl-Ludwig von Bezing, Roger D. Dixon, Demetrius Pohl, Greg Cavallo: The Kalahari manganese field: An update . In: The Mineralogical Record . tape 22 , no. 4 , 1991, pp. 279-297 (English).
  7. ↑ Wendell E. Wilson, Pete J. Dunn: Famous localities: The Kalahari manganese field . In: The Mineralogical Record . tape 9 , no. 3 , 1978, p. 137-153 (English).
  8. ↑ Vonbezingite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 67  kB ; accessed on February 9, 2018]).
  9. ↑ Mindat - Number of localities for Vonbezingit
  10. ↑ List of localities for Vonbezingit in the Mineralienatlas and Mindat
  11. ↑ Mindat - Vonbezingit