Molybdofornacite
A valid IMA mineral species
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About Molybdofornacite
Formula:
Pb2Cu(MoO4,CrO4)(AsO4,PO4)(OH)
Colour:
Light green, olive green
Lustre:
Adamantine, Sub-Adamantine, Vitreous, Resinous, Greasy
Hardness:
3 - 4
Specific Gravity:
6.57
Crystal System:
Monoclinic
Name:
Named for its relationship to fornacite, but with molybdenum dominant over chromium.
Isostructural with:
Unique Identifiers
Mindat ID:
2734
Long-form identifier:
mindat:1:1:2734:8
IMA Classification of Molybdofornacite
Approved
IMA Formula:
Cu2+Pb2+2Mo6+O4As5+O4(OH)
Approval year:
1982
First published:
1983
Classification of Molybdofornacite
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
43.4.3.3
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
22.5.5
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 |
|---|---|---|
| Mfor | 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 Molybdofornacite
Adamantine, Sub-Adamantine, Vitreous, Resinous, Greasy
Transparency:
Transparent, Translucent
Colour:
Light green, olive green
Streak:
Pale Yellow
Hardness:
3 - 4 on Mohs scale
Tenacity:
Brittle
Cleavage:
None Observed
Fracture:
Conchoidal
Density:
6.57 g/cm3 (Measured) 6.6 g/cm3 (Calculated)
Optical Data of Molybdofornacite
Type:
Biaxial (+)
RI values:
nα = 2.05(2) nγ = 2.15(2)
Birefringence:
0.10
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:
r < v strong
Pleochroism:
Strong
Comments:
X and Y pale yellow, Z green yellow.
Chemistry of Molybdofornacite
Mindat Formula:
Pb2Cu(MoO4,CrO4)(AsO4,PO4)(OH)
Element Weights:
Crystallography of Molybdofornacite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/b
Setting:
P21/c
Cell Parameters:
a = 8.100(5) Å, b = 5.946(3) Å, c = 17.651(1) Å
β = 109.17(5)°
β = 109.17(5)°
Ratio:
a:b:c = 1.362 : 1 : 2.969
Unit Cell V:
802.98 ų (Calculated from Unit Cell)
Z:
4
Twinning:
Rare “butterfly” contact twins, at 120 degrees.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.27 Å | (10) |
| 4.84 Å | (50) |
| 4.50 Å | (5) |
| 4.15 Å | (30) |
| 4.06 Å | (20) |
| 3.78 Å | (10) |
| 3.41 Å | (40) |
| 3.32 Å | (100) |
| 3.23 Å | (5) |
| 3.11 Å | (3) |
| 2.979 Å | (60) |
| 2.937 Å | (40) |
| 2.845 Å | (60) |
| 2.753 Å | (60) |
| 2.635 Å | (10) |
| 2.555 Å | (5) |
| 2.460 Å | (5) |
| 2.433 Å | (10) |
| 2.353 Å | (50) |
| 2.149 Å | (3) |
| 2.093 Å | (30) |
| 2.070 Å | (3) |
| 2.006 Å | (30) |
| 1.914 Å | (20) |
| 1.898 Å | (10) |
| 1.864 Å | (20) |
| 1.795 Å | (10) |
| 1.776 Å | (10) |
| 1.670 Å | (30) |
| 1.624 Å | (10) |
Comments:
ICDD 35-593.
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] | |
| 47h : [Near-surface oxidized, dehydrated minerals] |
Type Occurrence of Molybdofornacite
General Appearance of Type Material:
Minute lath-like crystals on dioptase
Place of Conservation of Type Material:
Mineralogical Institute, Ruhr-University, Bochum, Germany.
Geological Setting of Type Material:
Oxidation zone
Associated Minerals at Type Locality:
Synonyms of Molybdofornacite
Other Language Names for Molybdofornacite
Common Associates
Associations Based on Photo Data:
| 23 photos of Molybdofornacite associated with Wulfenite | Pb(MoO4) |
| 19 photos of Molybdofornacite associated with Malachite | Cu2(CO3)(OH)2 |
| 13 photos of Molybdofornacite associated with Dioptase | CuSiO3 · H2O |
| 12 photos of Molybdofornacite associated with Quartz | SiO2 |
| 4 photos of Molybdofornacite associated with Mimetite | Pb5(AsO4)3Cl |
| 3 photos of Molybdofornacite associated with Chalcocite | Cu2S |
| 2 photos of Molybdofornacite associated with Pyromorphite | Pb5(PO4)3Cl |
| 2 photos of Molybdofornacite associated with Hemimorphite | Zn4Si2O7(OH)2 · H2O |
| 2 photos of Molybdofornacite associated with Anglesite | PbSO4 |
| 2 photos of Molybdofornacite associated with 'Limonite' |
Related Minerals - Strunz-mindat Grouping
| 7.FC.05 | Vauquelinite | Pb2Cu(CrO4)(PO4)(OH) |
| 7.FC.10 | Fornacite | Pb2Cu(CrO4)(AsO4)(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 Molybdofornacite
Not known to fluoresce in UV
Other Information
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 Molybdofornacite
mindat.org URL:
https://www.mindat.org/min-2734.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 Molybdofornacite
Reference List:
Dunn, Pete J., Chao, George Y., Grice, Joel D., Ferraiolo, James A., Fleischer, Michael, Pabst, Adolf, Zilczer, Janet A. (1984) New mineral names. American Mineralogist, 69 (5-6) 565-569
Localities for Molybdofornacite
Showing 23 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.
Chile | |
| Maurizio Dini collection |
| Maurizio Dini collection (material analysed by Dr. Jochen Schlüter) +1 other reference |
France | |
| N. Meisser (XRD and SEM-EDS analyses) +1 other reference |
Germany | |
| Collection of Steffen Michalski |
Mexico | |
| Andreas SChloth collection (XRD-analysed by Sid Williams) |
Morocco | |
| Favreau (2026) |
Namibia (TL) | |
| Medenbach et al. (1983) |
Spain | |
| Calvo Rebollar et al. (2022) |
Switzerland | |
| Ansermet (2012) |
USA | |
| Ron Layton self collected |
| Peter Megaw |
| Peter Mcgaw | |
| Anthony et al. (1995) |
| Frost et al. (2007) |
| e-rocks.com (n.d.) |
| Allen et al. (1988) +1 other reference |
| Thorne (n.d.) |
| Collection of John Dagenais |
| Collected by Sugar White. In the ... |
| Dr. William S. Wise presentation to ... |
| Castor et al. (2004) |
| DeMark (1989) |
| Walstrom (n.d.) +2 other references |
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Alice Mine, Goodsprings, Goodsprings Mining District, Spring Mountains, Clark County, Nevada, USA