Fornacite
A valid IMA mineral species - grandfathered
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About Fornacite
Lucien Louis Fourneau
Formula:
Pb2Cu(CrO4)(AsO4)(OH)
Colour:
Deep olive-green; golden yellow in transmitted light (small grains).
Lustre:
Resinous, Waxy, Greasy
Hardness:
2 - 3
Specific Gravity:
6.27
Crystal System:
Monoclinic
Name:
Named in 1916 by Antoine François Alfred Lacroix from the Latin fornax "the furnace" in honor of geographer and French colonial governor of Middle Congo (1911-16), Lucien Louis Fourneau [February 16, 1867, Saint-Cyr-l'Ecole, Yvelines, France - August 3, 1930, Perros-Guirec, Côtes-du-Nord [now Côtes-d'Armor], France], whose name also translates to "the furnace".
Fourneau was lieutenant governor of Oubangui-Chari (1909-10) and commissioner of French Cameroons (1916-19).
Fourneau was lieutenant governor of Oubangui-Chari (1909-10) and commissioner of French Cameroons (1916-19).
Type Locality:
Isostructural with:
Fornacite-Vauquelinite Series. The arsenate analogue of vauquelinite.
Related to the Brackebuschite Supergroup.
Related to the Brackebuschite Supergroup.
Unique Identifiers
Mindat ID:
1583
Long-form identifier:
mindat:1:1:1583:3
IMA Classification of Fornacite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Cu2+Pb2+2(Cr6+O4)(As5+O4)(OH)
First published:
1915
Classification of Fornacite
7.FC.10
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
C : With PO4, AsO4, SiO4
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
C : With PO4, AsO4, SiO4
43.4.3.2
43 : COMPOUND PHOSPHATES, ETC.
4 : Anhydrous Compound Phosphates, etc·, Containing Hydroxyl or Halogen
43 : COMPOUND PHOSPHATES, ETC.
4 : Anhydrous Compound Phosphates, etc·, Containing Hydroxyl or Halogen
22.5.4
22 : Phosphates, Arsenates or Vanadates with other Anions
5 : Phosphates, arsenates or vanadates with chromate, molybdate, niobate or tantalate
22 : Phosphates, Arsenates or Vanadates with other Anions
5 : Phosphates, arsenates or vanadates with chromate, molybdate, niobate or tantalate
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| For | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Fornacite
Resinous, Waxy, Greasy
Transparency:
Transparent
Colour:
Deep olive-green; golden yellow in transmitted light (small grains).
Streak:
Olive green
Hardness:
2 - 3 on Mohs scale
Tenacity:
Brittle
Fracture:
Irregular/Uneven, Conchoidal, Sub-Conchoidal
Density:
6.27 g/cm3 (Measured) 6.30 g/cm3 (Calculated)
Optical Data of Fornacite
Type:
Biaxial (+)
RI values:
nα = 2.142 nγ = 2.242
Birefringence:
0.100
Max. Birefringence:
δ = 0.100
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Very High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
No measured or calculated 2V is on file for this mineral, so the value used here (92°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
No measured or calculated 2V is on file for this mineral, so the value used here (92°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Dispersion:
Strong
Pleochroism:
Non-pleochroic
Comments:
2V rather large.
Chemistry of Fornacite
Mindat Formula:
Pb2Cu(CrO4)(AsO4)(OH)
Element Weights:
Crystallography of Fornacite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/b
Setting:
P121/c1
Cell Parameters:
a = 8.101(2) Å, b = 5.893(11) Å, c = 17.547(9) Å
β = 110.00(4)°
β = 110.00(4)°
Ratio:
a:b:c = 1.375 : 1 : 2.978
Unit Cell V:
787.16 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Short bladed crystals in divergent groupings.
Comment:
Other cell given: 7.91, 5.91, 17.46 A, xxx°.
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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View
CIF File Best | x | y | z | a | b | c
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Rotation
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Labels
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0010641 | Fornacite | Cocco G, Fanfani L, Zanazzi P F (1967) The crystal structure of fornacite Zeitschrift fur Kristallographie 124 385-397 |  | 1967 | Reneville, Congo | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.22 Å | (50) |
| 4.80 Å | (90) |
| 3.31 Å | (100) |
| 2.98 Å | (100) |
| 2.88 Å | (100) |
| 2.80 Å | (100) |
| 2.71 Å | (90) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47d : [Arsenates, antimonates, selenates, bismuthinates] | |
| 47e : [Vanadates, chromates, manganates] |
Geological Setting:
Oxidized zones of polymetallic deposits
Type Occurrence of Fornacite
General Appearance of Type Material:
Confused groups of small, prismatic crystals.
Place of Conservation of Type Material:
Muséum Nationale d’Histoire Naturelle, Paris, France, number 114.145.
Associated Minerals at Type Locality:
Synonyms of Fornacite
Other Language Names for Fornacite
Relationship of Fornacite to other Species
Forms a series with:
Common Associates
Associations Based on Photo Data:
| 93 photos of Fornacite associated with Mimetite | Pb5(AsO4)3Cl |
| 89 photos of Fornacite associated with Wulfenite | Pb(MoO4) |
| 80 photos of Fornacite associated with Chrysocolla | Cu2-xAlx(H2-xSi2O5)(OH)4 · nH2O, x < 1 |
| 71 photos of Fornacite associated with Dioptase | CuSiO3 · H2O |
| 61 photos of Fornacite associated with Quartz | SiO2 |
| 34 photos of Fornacite associated with Willemite | Zn2SiO4 |
| 23 photos of Fornacite associated with Malachite | Cu2(CO3)(OH)2 |
| 21 photos of Fornacite associated with Iranite | Pb10Cu(CrO4)6(SiO4)2(OH)2 |
| 21 photos of Fornacite associated with Fluorite | CaF2 |
| 20 photos of Fornacite associated with Cerussite | PbCO3 |
Related Minerals - Strunz-mindat Grouping
| 7.FC.05 | Vauquelinite | Pb2Cu(CrO4)(PO4)(OH) |
| 7.FC.10 | Molybdofornacite | Pb2Cu(MoO4,CrO4)(AsO4,PO4)(OH) |
| 7.FC.15 | Hemihedrite | Pb10Zn(CrO4)6(SiO4)2(OH)2 |
| 7.FC.15 | Raygrantite | Pb10Zn(SO4)6(SiO4)2(OH)2 |
| 7.FC.15 | Iranite | Pb10Cu(CrO4)6(SiO4)2(OH)2 |
| 7.FC.20 | Embreyite | Pb5(CrO4)2(PO4)2 · H2O |
| 7.FC.20 | Cassedanneite | Pb5(CrO4)2(VO4)2 · H2O |
Fluorescence of Fornacite
Not Fluorescent in UV.
Other Information
Notes:
Totally soluble in HCl.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Fornacite
mindat.org URL:
https://www.mindat.org/min-1583.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
External Links:
Mineral Dealers:
References for Fornacite
Reference List:
Lacroix, Alfred (1915) Note préliminaire sur une nouvelle espèce minérale (furnacite) provenant du Moyen Congo. Bulletin de la Société Française de Minéralogie, 38 (5). 198-200 doi:10.3406/bulmi.1915.3624
Bariand, Pierre, Herpin, Paulette (1962) Nouvelles données sur la fornacite (chromo-arséniate de plomb et de cuivre) Bulletin de Minéralogie, 85 (3) 309-311 doi:10.3406/bulmi.1962.5584
Cocco, G., Fanfani, L., Zanazzi, P. F. (1967) The crystal structure of fornacite. Zeitschrift für Kristallographie - Crystalline Materials, 124 (6) 385-397 doi:10.1524/zkri.1967.124.6.385
Fanfani, L., Zanazzi, P. F. (1967) Structural similarities of some secondary lead minerals. Mineralogical Magazine and Journal of the Mineralogical Society, 36 (280) 522-529 doi:10.1180/minmag.1967.036.280.06
Cesbron, Fabien, Williams, Sydney A. (1980) Iranite˗hémihédrite, bellite, phoenicochroite, vauquelinite et fornacite : synthèse et nouvelles données. Bulletin de Minéralogie, 103 (5) 469-477 doi:10.3406/bulmi.1980.7409
Localities for Fornacite
Showing 124 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Australia | |
| Birch et al. (1997) |
| Nickel et al. (1994) +1 other reference |
| Nickel (1982) |
Chile | |
| samples analysed by Gerhard Mohn and ... |
| T. Kampf analysis |
| Maurizio Dini & Robert Jenkins ... +1 other reference |
Czech Republic | |
| Pauliš et al. (2023) |
France | |
| Thierry Brunsperger collection |
| Patrice Queneau Collection. Visual ... |
Germany | |
| Lapis (10) |
| |
| Legner et al. (2022) |
| Gerhard Möhn Collection Analyzed by ... |
| Leonhardt et al. (1991) |
Greece | |
| Fritz Schrieber |
| Branko Rieck |
| Rieck (n.d.) |
| Schnorrer (1995) +2 other references | |
| Blaß et al. (1998) | |
| Rieck (n.d.) |
| Rieck (n.d.) +2 other references | |
| Hanke (1998) | |
| Wendel et al. (1999) | |
Hungary | |
| Szakáll: Minerals of Szár Hill +1 other reference |
Iran | |
| Bariand |
| Bariand et al. (1963) | |
| Bariand et al. (1980) |
Italy | |
| SEM/EDS 18/09/2001 MNHN-Paris |
| Dini et al. (2013) |
Mexico | |
| Braith et al. (2001) +1 other reference |
| Alejandro Felix Gutierrez Collection |
Morocco | |
| Favreau et al. (2006) |
Namibia | |
| Swakop Uranium |
| Min. Record (in press) |
Republic of the Congo | |
| Lacroix (1915) +1 other reference |
| EDXS analyses by P. Roth | |
| Andreas Sloth collection | |
Russia | |
| webmineral.ru (2020) |
| Клейменов Д.А. +1 other reference |
| Pavel M. Kartashov analytical data (2012) |
| Dmitry A. Khanin |
South Africa | |
| Cairncross et al. (1995) |
| Reeks (2007) |
Switzerland | |
| Ansermet et al. (2021) |
UK | |
| Turner (2006) +3 other references |
USA | |
| Graeme (1981) +1 other reference |
| Luetcke (n.d.) |
| Rob Bowell |
| Robert Jenkins Raman Spectroscopy |
| Anthony et al. (1995) +1 other reference |
| Williams (1981) |
| Mineral collected by Jerry A. Baird |
| Hunt (1983) |
| Anthony et al. (1995) |
| XRD analysis by Dr. Anthony Kampf. |
| Paul M. Adams Collection | |
| Luetcke (n.d.) |
| Mineral News (2002) +1 other reference |
| EDS analysis Association Jean WYART |
| Yang et al. (2013) | |
| Anthony et al. (1995) |
| Anthony et al. (1995) |
| Luetcke (n.d.) |
| Luetcke (n.d.) |
| Anthony et al. (1995) |
| Bideaux et al. (1960) +2 other references |
| Anthony et al. (1995) |
| Luetcke (n.d.) |
| Bideaux et al. (1960) +2 other references |
| Luetcke (n.d.) |
| Thorne (n.d.) |
| Anthony et al. (1995) |
| R. D. Green | |
| Luetcke (n.d.) |
| Anthony et al. (1995) |
| Mineralogical Society of America - ... |
| Cooper |
| Steve Stuart. +1 other reference |
| Raman ID 12-13-2007 on material ... +2 other references |
| Adams (2001) |
| Kampf et al. (2010) |
| Joe Marty specimens | |
| Thorne (n.d.) | |
| Collected by and in the collection of ... | |
| Housley R. | |
| Thorne (n.d.) | |
| The Blue Bell Claims San Bernardino ... |
| Thorne (n.d.) | |
| Collected by and in the collection of ... | |
| Ream (2004) |
| Thorne (n.d.) |
| www.mineralnews.com (2002) |
| Richard W. Thomssen +1 other reference |
| Castor et al. (2004) |
| Luetcke (n.d.) | |
| Dr. Robert Housley |
| Collected by Joe Marty | |
| Marek Chorazewicz (2025) |
| Castor et al. (2004) | |
| Haynes (2007) | |
| Castor et al. (2004) |
| Thorne (n.d.) | |
| John Hagstrom collection | |
| Castor et al. (2004) +1 other reference | |
| Thorne (n.d.) | |
| Castor et al. (2004) |
| Castor et al. (2004) |
| Robert E.Walstrom Collection +1 other reference | |
| Dr. William S. Wise presentation to ... |
| Marek Chorazewicz (2025) |
| Castor et al. (2004) |
| R&M 77:5 p298-305 +1 other reference |
| Northrop et al. (1996) | |
| Walstrom 2006 New Mexico Mineral ... |
| Northrop et al. (1996) |
| Walstrom (n.d.) |
| Walstrom (n.d.) | |
| Northrop et al. (1996) |
| Northrop et al. (1996) |
| Northrop et al. (1996) |
| Jay Penn collection | |
| Ron Layton |
Uzbekistan | |
| Pavel M. Kartashov (n.d.) |
Quick NavTopAbout FornaciteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesRelationshipsCommon AssociatesStrunz-MindatFluorescence Other InformationInternet Links References Localities Locality List
Eagle Eye Mine, Moore Mine group, New Water Mining District, New Water Mountains, La Paz County, Arizona, USA