Fornacite

Fornacite
	Greenish-yellow fornacite together with dioptase and cerussite from the Renéville Mines (Djoué Mines), Republic of the Congo (field of view 8 × 7 cm)
General and classification
other names	Furnacit; chromo-arseniate de plomb et de cuivre;
chemical formula	Pb 2 Cu [OH \| CrO 4 \| AsO 4 ]; Pb 2 Cu (AsO 4 ) (CrO 4 ) (OH);
Mineral class; (and possibly department)	Sulphates, Selenates, Tellurates, Chromates, Molybdates and Wolframates
System no. to Strunz ; and to Dana	7.FC.10 ( 8th edition : VI / F.02) ; 04/43/03/02
Similar minerals	Vauquelinite, molybdofornacite
Crystallographic Data
Crystal system	monoclinic
Crystal class ; symbol	monoclinic prismatic; 2 / m
Space group	P 2 1 / c (No. 14)
Lattice parameters	a = 8.10 Å ; b = 5.89 Å; c = 17.55 Å ; β = 110.0 °
Formula units	Z = 4
Physical Properties
Mohs hardness	3
Density (g / cm 3 )	6.27 (measured); 6.30 (calculated)
Cleavage	no
Break ; Tenacity	clamshell; brittle
colour	deep olive green, greenish yellow (golden yellow in transmitted light)
Line color	canary yellow, saffron yellow
transparency	transparent to translucent
shine	Greasy gloss, glass gloss
Crystal optics
Refractive indices	n α = 2.14 ± 0.02 ; n β = not defined ; n γ = 2.24 ± 0.02
Birefringence	δ = 0.10
Optical character	biaxial positive
Axis angle	2V = large
Pleochroism	weak
Other properties
Chemical behavior	Completely soluble in nitric acid

Fornacite is a rarely occurring mineral from the mineral class of " sulfates (including selenates , tellurates , chromates and tungstates )" with the chemical formula Pb ₂ Cu [OH | CrO ₄ | AsO ₄ ]. This makes the mineral a lead - copper - chromate - arsenate with additional hydroxide ions (OH ^- ).

Fornacit crystallizes in the monoclinic crystal system and develops up to 6 mm long, typically steep pyramidal and rounded crystals that always come together to form aggregates . They show a glass to greasy gloss and high light refraction and double refraction .

Etymology and history

In 1915, Antoine François Alfred Lacroix published a short note in which he described small olive-green crystals from the pits of Djoué (Renéville Mine) in what was then the French Congo in a “magnifique géode de dioptase”. Although only very little sample material was available, he interpreted his qualitative analyzes in such a way that a mineral similar to vauquelinite was present, in which most of the phosphate was replaced by arsenate. Lacroix named the mineral (derived from the Latin fornax for "furnace") in honor of the French geographer Lucien Louis Fourneau (1867-1930), lieutenant governor of Ubangi-Shari (1909-1910), governor of the Central Congo (1911-1916) and high commissioner and governor of French Cameroon (1916–19). The mineral was not described in more detail until 1951 and both its independence and the isotype with vauquelinite were proven. Both had previously been questioned by Edward Salisbury Dana and Hugo Strunz . Further processing took place in 1962 by Pierre Bariand and P. Herpin .

Although Antoine Lacroix used a stage from the Muséum national d'histoire naturelle in Paris to characterize the fornacite for the first time, type material is not strictly defined.

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the fornacite belonged to the mineral class of "sulfates, chromates, molybdates, wolframates" (as well as some selenates and tellurates) and there to the department of "chromates", where it belongs together Deaesmithite , edoylerite , molybdofornacite , phoenicochroit , santanaite , vauquelinite and wattersite form the "Phoenicochroit-vauquelinite group" with system no. VI / F.02 formed.

The 9th edition of Strunz's mineral systematics, valid since 2001 and used by the International Mineralogical Association (IMA), assigns fornacite to the class of "sulfates (including selenates, tellurates, chromates, molybdates and wolframates)" and there in the department of "Chromate". However, this is further subdivided according to the possible presence and type of additional anions, so that the mineral can be found according to its composition in the sub-section "With PO ₄ , AsO ₄ , SiO ₄ ", where, together with molybdofornacite, the " Fornacit group "with the system no. 7.FC.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Fornacit to the class of "phosphates, arsenates and vanadates" and there in the department of " phosphates ". Here he is in the " vauquelinite group " with the system no. 43.04.03 and the other members vauquelinit and molyddofornacit can be found in the subsection “Compound phosphates etc., (anhydrous compound anions with hydroxyl or halogen)”.

Crystal structure

Fornacite crystallizes in the monoclinic crystal system in the space group P 2 ₁ / c (space group no. 14) with the lattice parameters a = 8.10 Å ; b = 5.89 Å; c = 17.55 Å and β = 110.0 ° as well as four formula units per unit cell . Template: room group / 14

Fornacite is isotypic (isostructural) to vauquelinite and molybdofornacite, ie it crystallizes with the same crystal structure as vauquelinite. In the fornacite, the two non-equivalent Pb ions are surrounded by nine O atoms. The Cu ²⁺ ion has the coordination 4 + 2. (As, P) and Cr are tetrahedrally surrounded by O atoms. The structure of the Fornacits can be considered as made up of thick layers of edge-connected Pb ^[9] - polyhedron , parallel to (001) by z ≈ 0 and C / 2, and of zig-zag chains of edge-related CuO ₄ (OH) ₂ -Pseudo- octahedra describe parallel [010] (along the screw axis). The AsO ₄ - and CrO ₄ - tetrahedron link the layers of the Pb-polyhedra and the Cu-chains into a three dimensional network. The lack of preferred directions also explains the poor cleavage of the mineral.

The South African chemist professor emeritus Jan CA Boeyens wrote a limerick on fornacite and its crystal structure entitled "A mineral called fornacite" (A mineral called fornacite):

"The space group of fornacite / has a screw-axis at every site / And they operate such / to remind very much / Of what minerals do in the night ..."

"The Fornacit space group / has a screw axis at every position / And that is what it does / to remind / what minerals do at night ..."

properties

morphology

Fornacite forms up to 6 mm long, prismatic, typically steep pyramidal and rounded crystals , which always come together to form aggregates of jumbled crystals. At the type locality, these groups sit on Dioptas.

physical and chemical properties

The crystals of the fornacite are deep green to greenish-yellow, the line color of the mineral is z. T. as canary yellow, z. T. described as saffron yellow. The transparent crystals have a pronounced fat-like sheen , which is also reflected in the comparatively high light refraction of 2.14 to 2.24 and the corresponding birefringence of 0.1. The mineral is not cleavable , but due to its brittleness it breaks like glass or quartz , with the fracture surfaces being formed like a shell. With a Mohs hardness of 3, Fornacite is one of the medium-hard minerals that, like the reference mineral calcite, can be scratched by a copper coin. The calculated density is 6.30 g / cm³.

Fornacit is completely soluble in nitric acid. It melts in the flame of the Bunsen burner while boiling to a greenish-black glass. In the process, water is given off, which can be regarded as basic, since no water escapes in the tube.

Modifications and varieties

Fornacite is the arsenate-dominant analogue of the phosphate-dominated vauquelinite and the chromium-dominated analogue of the molybdenum-dominated molybdofornacite. He is also related to the representatives of the Brackebuschit group.

Education and Locations

Fornacite forms secondarily in the oxidation zones of hydrothermal non-ferrous metal deposits. Minerals accompanying the fornacite in Djoué are dioptase, colorless mimetite, pyromorphite, cerussite, chalcosine, cuprite (chessylite), descloizit, mottramite, plancheit, vanadinite and willemite. In the Sébarz deposit, which became known in 1960, fornacite is found more or less closely accompanied by cerussite, malachite, azurite, diabolite, atacamite, dioptase, chrysocolla, hemimorphite, phenicochroit and iranite. Other well-known accompanying minerals of the fornacite are wulfenite, hemihedrite, shattuckite and fluorite. Fornacite has only been described as a rare mineral formation from a few sites. So far (as of 2016) around 90 sites are known. The type locality is the Renéville Mines (Djoué Mines), Renéville, Kindanba District, Pool Department , Republic of the Congo .

In Germany , Fornacit occurred in a silicified barite dike at point 16.1 on the Hohenstein cliff near Reichenbach , district of Lautertal (Odenwald) in the Odenwald , in the "Schmitt" dolomite quarry in the Altenmittlau district of Freigericht , Spessart , both Hesse , and in the "Callenberg-Nord" opencast mine 1 “near Callenberg not far from Glauchau , Saxony . Locations in Austria and Switzerland are unknown.

In Europe, the mineral is known from the "Schurf Crocoitovyi" of the Berjosowski gold deposit on Uspenskaja Mountain near Berjosowski not far from Yekaterinburg , Sverdlovsk Oblast , Urals , Russia , from the "Hilarion Mine" in the area of the Kamariza Mines near Agios Konstantinos and from various sites in Area of Sounion , all in the Lavrion District, Attica region , Greece , from the "Miniera di Traversella" near Traversella, Val Chiusella, Canavese District, Metropolitan City of Turin , Piedmont , and "Campo alle Buche" near Campiglia Marittima , Monti del Campigliese, Province Livorno , Tuscany , both Italy and from the “Torr Works (Merehead) Quarry” near Cranmore, Somerset , England , United Kingdom .

In Asia from the "Sebarz Mine" and "Chah Khouni Mine", both at Nain in Shah residue at Anarak, Province of Isfahan , and the "visual Changi Mine" at Neybaud, Khorasan Province Yazd , Iran . From the “Almalyk Mine” near Olmaliq not far from Tashkent , Uzbekistan . In Africa from the “Oumlil Mine” near Taznakht in the Bou Azzer District, Ouarzazate Province , Drâa-Tafilalet Region , Morocco , the “Tsumeb Mine” (Tsumcorp Mine) in Tsumeb , Oshikoto Region , and the Husab opencast mine , Erongo Region , both Namibia , and from the Pb-Zn mines of "Argent", Transvaal , South Africa, about 100 km east of Johannesburg .

In America from the "Miniera Dulcinea de Llampos", District Cachiyuyo de Llampos, Province Copiapó , Región de Atacama , Chile , the "Moctezuma (Bambolla) Mine" near Moctezuma , Sonora , Mexico, as well as a large number of sites in the United States . In Arizona, these include the "Mammoth-Saint Anthony Mine" near Tiger, Pinal County , the "Tonopah-Belmont Mine" near Belmont Mountain, Tonopah , Osborn District, Big Horn Mts, Maricopa County , and the "Lone Star Mine" near Copperopolis , Yavapai County , the 79 Mine, Gila County , the Shattuck Mine at Bisbee, Warren District, Cochise County, and the Eagle Eye Mine, New Water Mts, La Paz County ; in California, the "Blue Bell Mine" near Baker, San Bernardino County ; in New Mexico the “Socorro Peak” and the “Bullfrog No. 1, 3 km northwest of Magdalena near Silver Hill”. 2 Mine ", North Magdalena District, both Socorro County , and finally the" Killie Mine ", Spruce Mountain District, Elko County and the" Silver Coin Mine "at Valmy, Iron Point District, Humboldt Co. , both in Nevada .

In Australia from the Teutonic Bore deposit located 300 km north of Kalgoorlie , and from Whim Creek east of Roebourne , Pilbara region , both in Western Australia .

use

With a PbO content of around 56% by weight, Fornacit would be a rich lead ore. Due to its extreme rarity, however, the mineral is only of interest to collectors.

literature

Pierre Bariand, P. Herpin: Nouvelles données sur la fornacite (chromo-arséniate de plomb et de cuivre). In: Bulletin de la Société française de minéralogie. Volume 85, 1962, pp. 309-311.
Claude Guillemin, J. Prouvost: Étude de la serie: fornacite – vauquelinite. In: Bulletin de la Société française de minéralogie. Volume 74, 1951, pp. 432-438.
Antoine Lacroix : Note préliminaire une nouvelle espèce minérale (furnacite), provenant du Moyen Congo (Afrique équatoriale française). In: Bulletin de la Société Française de Minéralogie. Volume 38, 1915, pp. 198-200.
Fornacite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF, 64 kB ).

Web links

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

Individual evidence

↑ ^a ^b ^c ^d ^e 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. 417 .
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l Fornacite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF 65 kB ).
↑ ^a ^b ^c ^d ^e ^f ^g ^h Claude Guillemin, J. Prouvost: Étude de la série: fornacite – vauquelinite. In: Bulletin de la Société française de minéralogie. Volume 74, 1951, pp. 432-438.
↑ ^a ^b ^c Pierre Bariand, P. Herpin: Nouvelles données sur la fornacite (chromo-arséniate de plomb et de cuivre). In: Bulletin de la Société française de minéralogie. Volume 85, 1962, pp. 309-311.
↑ ^a ^b ^c ^d ^e ^f ^g ^h Antoine Lacroix : Note préliminaire une nouvelle espèce minérale (furnacite), provenant du Moyen Congo (Afrique équatoriale française). In: Bulletin de la Société Française de Minéralogie. Volume 38, 1915, pp. 198-200 ( PDF, 167 kB ).
↑ ^a ^b http://www.mindat.org/min-1583.html Mindat - Fornacit
^ G. Cocco, L. Fanfani, PF Zanazzi: The crystal structure of fornacite. In: Journal of Crystallography. Volume 124, 1967, pp. 385-397 ( PDF, 667 kB ).
↑ Rik Dillen: Mineraal van de maand fornaciet. In: geonieuws. Volume 34, Issue 9, 2009, pp. 213-216 ( PDF 1.26 MB ).
↑ Mindat - Number of localities for Fornacit
↑ ^a ^b List of localities for Fornacit in the Mineralienatlas and Mindat

[StrunzNickel-1] 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. 417 .

[Datenblatt-2] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l Fornacite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF 65 kB ).

[Guillemin-3] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Claude Guillemin, J. Prouvost: Étude de la série: fornacite – vauquelinite. In: Bulletin de la Société française de minéralogie. Volume 74, 1951, pp. 432-438.

[BariandHerpin-4] Pierre Bariand, P. Herpin: Nouvelles données sur la fornacite (chromo-arséniate de plomb et de cuivre). In: Bulletin de la Société française de minéralogie. Volume 85, 1962, pp. 309-311.

[Lacroix-5] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Antoine Lacroix : Note préliminaire une nouvelle espèce minérale (furnacite), provenant du Moyen Congo (Afrique équatoriale française). In: Bulletin de la Société Française de Minéralogie. Volume 38, 1915, pp. 198-200 ( PDF, 167 kB ).

[mindat-6] ttp://www.mindat.org/min-1583.html Mindat - Fornacit

[Cocco-7] G. Cocco, L. Fanfani, PF Zanazzi: The crystal structure of fornacite. In: Journal of Crystallography. Volume 124, 1967, pp. 385-397 ( PDF, 667 kB ).

[Dillen-8] Rik Dillen: Mineraal van de maand fornaciet. In: geonieuws. Volume 34, Issue 9, 2009, pp. 213-216 ( PDF 1.26 MB ).

[MindatAnzahl-9] Mindat - Number of localities for Fornacit

[Fundorte-10] List of localities for Fornacit in the Mineralienatlas and Mindat