Cornubite

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Cornubite
Cornubite.jpg
Cornubit from the "Majuba Hill Mine", Antelope District, Nevada, USA (size: 5 cm)
General and classification
other names

Corunuvite

chemical formula Cu 5 [(OH) 4 | (AsO 4 ) 2 ]
Mineral class
(and possibly department)
Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana
8.BD.30 ( 8th edition : VII / B.11)
04.41.02.01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 6.121  Å ; b  = 6.251 Å; c  = 6.790 Å,
α  = 92.93 °; β  = 111.30 °; γ  = 107.47 °
Formula units Z  = 1
Physical Properties
Mohs hardness 4th
Density (g / cm 3 ) 4.64 (measured on fibrous aggregates); 4.85 (calculated)
Cleavage two cleavages intersecting at 70 °; both vertical (2 1 1)
Break ; Tenacity uneven, half-mussel
colour apple green, pale to dark green
Line color pale green
transparency translucent to translucent
shine Glass gloss, also resin, wax and fat gloss
Crystal optics
Refractive indices n α  = 1.87
n β  = not defined
n γ  = ≈ 1.90
Birefringence δ = 0.03
Optical character biaxial negative
Axis angle 2V = very large
Pleochroism not pleochroic

Cornubit is a seldom occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the triclinic crystal system with the composition Cu 5 [(OH) 4 | (AsO 4 ) 2 ], so from a chemical point of view it is a copper arsenate with additional hydroxide ions .

Cornubit occurs in the form of fibrous, grape-like and spherical mineral aggregates as well as porcelain-like masses. The up to 5 mm large, parallel {2 1 1} tabular crystals , however, are very rare. Crystals and aggregates typically show apple-green hues.

Etymology and history

Cornubit was first discovered in the English county of Cornwall in the United Kingdom , more precisely in the Wheal Carpenter deposit near Fraddam, Gwinear . The mineral was first described in 1959 by the English mineralogists Gordon Frank Claringbull , Max Hutchinson Hey and RJ Davis. They named the mineral after Cornubia, the medieval Latin name of the county of Cornwall. The type material of the mineral is kept in the Natural History Museum in London (register no. 1964R, 8650).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the cornubite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "anhydrous phosphates, with foreign anions F, Cl, O, OH", where, together with arsenoclasite , cornwallite , gatehouseit , ludjibaite , pseudomalachite , reichenbachite , reppiaite and turanite, it formed the unnamed group VII / B.11 .

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 cornubit to the category of “phosphates, etc. with additional anions; without H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the additional anions to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral is classified in the sub-section “With only medium-sized cations; (OH etc.): RO 4  = 2: 1 “can be found where it is the only member of the unnamed group 8.BD.30 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns cornubite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates, etc., with hydroxyl or halogen". Here it can be found together with Cornwallit in the unnamed group 41.04.02 within the sub-section " Anhydrous phosphates etc., with hydroxyl or halogen with (AB) 5 (XO 4 ) 2 Z q ".

Crystal structure

Cornubite crystallizes in the triclinic crystal system in the space group P 1 (space group no. 2) with the lattice parameters a  = 6.121  Å ; b  = 6.251 Å; c  = 6.790 Å; α = 92.93 °; β = 111.30 ° and γ = 107.47 ° and one formula unit per unit cell . Template: room group / 2

The crystal structure contains layers of edge- sharing CuO 6 octahedra parallel (0 1 1), which are linked to the AsO 4 tetrahedra via common corners and via hydrogen bonds.

properties

morphology

Cornubite generally occurs in the form of fibrous, grape-like and spherical aggregates as well as porcelain-like masses. At the Wheal Carpenter type locality, the mineral was found in apple-green, grape-shaped, internally fibrous aggregates on dark green, fibrous Cornwallite, which sat on well-crystallized quartz. In Reichenbach, tabular crystals with a maximum size of 0.3 mm × 0.3 mm and a thickness of up to 0.05 mm, often fused into irregular masses , appeared very rarely after {2 1 1}.

physical and chemical properties

The color of the cornubit is apple green, its stroke color is pale green. While the fibrous aggregates are silk gloss, the translucent crystals have a glass gloss. With a Mohs hardness of 4, cornubite is one of the medium-hard minerals that, like the reference mineral fluorite, can be easily scratched with a pocket knife. Two fissile properties can be observed on cornubite crystals, both perpendicular to (2 1 1): they are roughly parallel to (011) and ( 1 1 1) and intersect at an angle of about 70 °. The mineral has high refractive indices, which are difficult to determine due to the rapid reaction of the crystals with the immersion liquids. The calculated mean refractive index is 1.854. Cornubit is soluble in acids such as HCl and HNO 3 . It is potentially unstable in basic solutions.

Modifications and varieties

The compound Cu 5 [(OH) 4 | (AsO 4 ) 2 ] is dimorphic and occurs naturally in addition to the triclinic cornubite as monoclinic crystallizing cornwallite . Chemically, cornubite is the arsenate-dominant analogue of the phosphate-dominated minerals pseudomalachite, ludjibaite and rich bachite.

Education and Locations

Crusts of spherical cornubite aggregates up to 0.25 mm in diameter from the "Mine de Salsigne", Mas-Cabardès, Carcassonne, Aude, Occitania, France
Cornubite in spherical aggregates up to 0.3 mm in size and light green needle-like olivite crystals from the "Mina Grande" near Marqueza, Coquimbo region, Chile

Cornubit formed secondarily in the oxidation zone of hydrothermal, copper-tin-silver leading veins . Other copper phosphates or arsenates can occur as accompanying minerals . Are known Cornwallit , Chalkophyllit , Olivenit , Lirokonit , Chenevixit , Klinoklas , Pseudomalachit , Bayldonit , Parnauit , Tirolit and azurite , malachite , cuprite , chrysocolla and quartz . At the type locality, the mineral was found on Cornwallite, which itself sat on well-crystallized quartz. In Reichenbach, the dominant ore mineral chalcopyrite is almost completely transformed into chalcosine and malachite. The cornubit was accompanied by goethite in velvety coatings on quartz; blue-green pseudomalachite crystals; light blue needle-like agardite / mixite crystals; dark green tabular bayldonite crystals; light green prismatic Duftite crystals; colorless to bluish Hinsdalite crystals and possibly also tsumcorite. The age relationship between the associated minerals is quartz → goethite → cornubite + pseudomalachite → agardite / mixite.

As a rare mineral formation, cornubite could only be detected at a few sites. So far (as of 2016) around 120 sites are known. In addition to its type locality , the Wheal Carpenter pit at Gwinear, the mineral also occurred in the United Kingdom in the Wheal Gorland, Wheal Unity and Wheal Muttrell pits, all in the Gwennap Mining District near Camborne; the "Phoenix United Mine" at Linkinghorne; the "East Gunnislake Mine" at Calstock, the "Penberthy Croft Mine" at St Hilary , the " Botallack Mine " at St Just in Penwith (all in Cornwall), as well as in the "Bedford United Mine" and in "Devon Great Consols" , both near Tavistock (Devon) in Devon (England) , in the "Old Potts Gill Mine", Caldbeck Fells, Cumbria , and on the Southwick Cliffs near Dalbeattie , Dumfries and Galloway , Scotland .

In Germany , the mineral came next to the first place of discovery for cornubite crystals, the point 8.0 on the Borsteinklippe near Reichenbach , district of Lautertal (Odenwald) in the Odenwald ([Hessen]), in the same silicified barite dike also at point 16.1 in the vicinity of the Hohenstein in front. Other German sites from Baden-Württemberg are the “Silberbrünnle” mine in the Haigerach Valley near Gengenbach , the Clara mine in the Rankach Valley near Oberwolfach and Neubulach, all in the Black Forest , from North Rhine-Westphalia the “Leibnitz-Dante” mine and from the winner country the pits "Eisenzecher train" at Eiserfeld , "Sophie" in Gosenbach , "Old Buntekuh" at Niederschelden and "Käusersteimel" at Kausen and from Saxony , the pit father Abraham in Lauta to name.

In Austria , Cornubit has so far been found on the Gratlspitz near Brixlegg in Tyrol . As discovery sites in Switzerland are the Mürtschenalp , Canton Glarus , Six-Blanc in Bruson (municipality of Bagnes ) and the Wannigletscher in the Binn Valley, both of Valais , is known. From France from the Cap Garonne mine near Le Pradet, Var , from the copper mines of Roua, Alpes-Maritimes , about 50 km north of Nice , and from the “Mine de Salsigne”, Mas-Cabardès, Carcassonne , Aude , Occitania . From Slovakia from Farbište near Ponická Huta and from Svätodušná near Ľubietová (Libethen) not far from Banská Bystrica (Neusohl). From the Monte Nero mine at Rocchetta Vara, La Spezia Province , Liguria , Italy . From the La Reconquistada claim at the “Mina Dolores”, Pastrana , Mazarrón - Águilas , Murcia , Spain .

In the United States from the Centennial Eureka Mine, Tintic District, Juab Co. , and from Gold Hill, Tooele Co. , both Utah , from the Majuba Hill Mine, Antelope District, Pershing Co. , Nevada , from the vicinity of the "Humboldt" and "Marshall Mines", Santa Cruz Co. , Arizona , as well as from Sylvanite, Hidalgo Co. , and the "Buckhorn Mine", Red Cloud District, Lincoln Co. , both New Mexico . From the "Guanaco" deposit near Santa Catalina , Región de Antofagasta , and the "Mina Grande" near Marqueza, Arqueros silver mining district, La Serena , Coquimbo region , Chile . Small crystals also from Ashburton Downs Station, Western Australia , Australia . In the Democratic Republic of the Congo (Zaïre) from the “Mindingi Mine” near Swambo, Province of Haut-Katanga .

Other locations include Greece, Hungary, Italy, Argentina, Australia, Bulgaria, China, France, Japan, Morocco, Poland, Spain and several states in the United States .

See also

literature

  • GF Claringbull, MH Hey and RJ Davis: Cornubite, a new mineral dimorphous with cornwallite . In: Mineralogical Magazine . tape 32 , 1959, pp. 1-5 .

Web links

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

Individual evidence

  1. a b c d e 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.  448 .
  2. a b c d e f g h i Cornubite . 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; 67  kB ; accessed on August 27, 2017]).
  3. a b c d e f Mindat - Cornubit
  4. a b c d e f g h i j Ekkehart Tillmanns, Wolfgang Hofmeister, Klaus Petitjean: Cornubite, Cu 5 (AsO 4 ) 2 (OH) 4 , first occurrence of single crystals, mineralogical description and crystal structure . In: Bull. Geol. Soc. Finland . tape 57 , 1985, pp. 119–127 ( rruff.info [PDF; 520 kB ; accessed on August 27, 2017]).
  5. ^ GF Claringbull, MH Hey, RJ Davis: Cornubite, a new mineral dimorphous with cornwallite . In: Mineralogical Magazine . tape 32 , 1959, pp. 1–5 ( rruff.info [PDF; 244 kB ; accessed on January 15, 2017]).
  6. Rudolf Duthaler, Stefan Weiß: Clean, prepare and store minerals. The workbook for the collector . 1st edition. Christian Weise Verlag, Munich 2008, ISBN 978-3-921656-70-9 , p. 139, 152 .
  7. Mindat - Number of locations for Cornubit
  8. ^ Y. Laurent, R. Pierrot: Sur la présence de cornubite au cap Garonne (Var) . In: Bull. Soc. fr. Mineral. tape 84 , 1961, pp. 318-319 (French).
  9. Find location list for Cornubit in the Mineralienatlas and Mindat