Geminite
A valid IMA mineral species
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About Geminite
Formula:
Cu2+(AsO3OH) · H2O
Also written as Cu(HAsO4).H2O.
Colour:
Light green to sea green
Lustre:
Vitreous
Hardness:
3 - 3½
Specific Gravity:
3.70
Crystal System:
Triclinic
Name:
Named by H. Sarp and P. Perroud in 1990. The name is derived from the Latin gemini, meaning twins, for the twinning observed in the mineral.
Visually similar and chemically and structurally close to krupičkaite.
"For some unknown reason, some geminite specimens turn blue and opaque. This occurred on 4 of my specimens from Cap Garonne and 3 from the Khder mine in the Bou Azzer district, all previously translucent and pale green or pale blue." (Georges Favreau, https://www.mindat.org/mesg-388179.html )
See also the Koritnigite Group.
Compare lednevite that can be treated as a "stoichiometric" P-analogue, but this is not a true analogy due to structural misfit.
"For some unknown reason, some geminite specimens turn blue and opaque. This occurred on 4 of my specimens from Cap Garonne and 3 from the Khder mine in the Bou Azzer district, all previously translucent and pale green or pale blue." (Georges Favreau, https://www.mindat.org/mesg-388179.html )
See also the Koritnigite Group.
Compare lednevite that can be treated as a "stoichiometric" P-analogue, but this is not a true analogy due to structural misfit.
Unique Identifiers
Mindat ID:
1671
Long-form identifier:
mindat:1:1:1671:7
Similar Names
| Gimnit | A synonym of 'Deweylite' |
| Gymnita | A synonym of Antigorite |
| Gymnite | A variety of Serpentine Subgroup |
IMA Classification of Geminite
Approved
IMA Formula:
Cu2+(As5+O3OH)·H2O
Approval year:
1988
First published:
1990
Classification of Geminite
8.CB.30
8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
B : With only medium-sized cations, RO4:H2O = 1:1
8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
B : With only medium-sized cations, RO4:H2O = 1:1
40.5.12.1
40 : HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
5 : AXO4·xH2O
40 : HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
5 : AXO4·xH2O
20.1.7
20 : Arsenates (also arsenates with phosphate, but without other anions)
1 : Arsenates of Cu
20 : Arsenates (also arsenates with phosphate, but without other anions)
1 : Arsenates of Cu
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 |
|---|---|---|
| Gem | 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 Geminite
Vitreous
Transparency:
Transparent
Colour:
Light green to sea green
Streak:
Pale green
Hardness:
3 - 3½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Perfect
{001}
{001}
Fracture:
Irregular/Uneven
Density:
3.70(2) g/cm3 (Measured) 3.63 g/cm3 (Calculated)
Optical Data of Geminite
Type:
Biaxial (+)
RI values:
nα = 1.656 nβ = 1.692 nγ = 1.770
2V:
Measured: 75° , Calculated: 72°
Max. Birefringence:
δ = 0.114
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.
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.
Dispersion:
weak
Pleochroism:
Weak
Comments:
α = β = colorless
γ = pale green to pale gray
γ = pale green to pale gray
Chemistry of Geminite
Mindat Formula:
Cu2+(AsO3OH) · H2O
Also written as Cu(HAsO4).H2O.
Also written as Cu(HAsO4).H2O.
Element Weights:
Elements listed:
Crystallography of Geminite
Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 6.63 Å, b = 8.11 Å, c = 15.73 Å
α = 92.01°, β = 93.87°, γ = 95.02°
α = 92.01°, β = 93.87°, γ = 95.02°
Ratio:
a:b:c = 0.818 : 1 : 1.94
Unit Cell V:
839.91 ų (Calculated from Unit Cell)
Z:
16
Morphology:
Tabular {001}, slightly elongate [100].
Twinning:
Twinned polysynthetically parallel to {001}.
Comment:
Non-standard space-group setting C1.
Crystal Structure
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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) |
|---|---|---|---|---|---|---|---|
| 0014670 | Geminite | Prencipe M, Pushcharovsky D Y, Sarp H, Ferraris G (1996) Comparative crystal chemistry of geminite Cu[AsO3OH]H2O and related minerals Moscow University Geology Bulletin 51 51-58 | 1996 | Salsigne mine, Carrassonne, Aude, France | 0 | 293 | |
| 0005467 | Geminite | Cooper M A, Hawthorne F C (1995) The crystal structure of geminite, Cu(AsO3OH)(H2O), a heteropolyhedral sheet structure The Canadian Mineralogist 33 1111-1118 |  | 1995 | Cap Garone, France | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.83 Å | (100) |
| 3.925 Å | (60) |
| 3.260 Å | (70) |
| 3.107 Å | (40) |
| 3.070 Å | (70) |
| 2.825 Å | (40) |
| 2.611 Å | (50) |
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] | |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 55 : Anthropogenic mine minerals |
Type Occurrence of Geminite
General Appearance of Type Material:
Abundant euhedral, intergrown crystals up to 0.3 x 0.06 mm.
Place of Conservation of Type Material:
Museum d'Histoire Naturelle de Geneve, Geneva, Switzerland.
Associated Minerals at Type Locality:
Synonyms of Geminite
Other Language Names for Geminite
Common Associates
Associations Based on Photo Data:
| 34 photos of Geminite associated with Yvonite | Cu(HAsO4) · 2H2O |
| 13 photos of Geminite associated with Pushcharovskite | K0.6Cu18[AsO2(OH)2]4[AsO3OH]10(AsO4)(OH)9.6 · 18.6H2O |
| 8 photos of Geminite associated with Native Bismuth | Bi |
| 4 photos of Geminite associated with Quartz | SiO2 |
| 4 photos of Geminite associated with Zdenĕkite | NaPbCu5(AsO4)4Cl · 5H2O |
| 2 photos of Geminite associated with Rapidcreekite | Ca2(SO4)(CO3) · 4H2O |
| 2 photos of Geminite associated with Lavendulan | NaCaCu5(AsO4)4Cl · 5H2O |
| 2 photos of Geminite associated with Arsenolite | As2O3 |
Related Minerals - Strunz-mindat Grouping
| 8.CB. | Krupičkaite | Cu6[AsO3(OH)]6 · 8H2O |
| 8.CB.X | Honzaite | Ni2(AsO3OH)2 · 5H2O |
| 8.CB.X | Redondite | AlPO4 · 2H2O |
| 8.CB.05 | Ermeloite | Al(PO4) · H2O |
| 8.CB.05 | Serrabrancaite | MnPO4 · H2O |
| 8.CB.10 | Nyholmite | Cd3Zn2(AsO3OH)2(AsO4)2 · 4H2O |
| 8.CB.10 | Villyaellenite | (Mn,Ca)Mn2Ca2(AsO3OH)2(AsO4)2 · 4H2O |
| 8.CB.10 | Giftgrubeite | CaMn2Ca2(AsO4)2(AsO3OH)2 · 4H2O |
| 8.CB.10 | Hureaulite | Mn2+5(PO3OH)2(PO4)2 · 4H2O |
| 8.CB.10 | Miguelromeroite | Mn2+5(AsO3OH)2(AsO4)2(H2O)4 |
| 8.CB.10 | 'UM1997-09-AsO:CaHMgZn' | (Mg,Ca,Zn)5(AsO4)2(HAsO4)2 · 4H2O |
| 8.CB.15 | Krautite | Mn(HAsO4) · H2O |
| 8.CB.20 | Cobaltkoritnigite | Co(AsO3OH) · H2O |
| 8.CB.20 | Magnesiokoritnigite | Mg(AsO3OH) · H2O |
| 8.CB.20 | Koritnigite | Zn(AsO3OH) · H2O |
| 8.CB.25 | Yvonite | Cu(HAsO4) · 2H2O |
| 8.CB.35 | Schubnelite | Fe3+VO4 · H2O |
| 8.CB.40 | Radovanite | Cu2Fe3+(AsO4)(HAs3+O3)2 · H2O |
| 8.CB.45 | Kazakhstanite | Fe3+5V4+3V5+12O39(OH)9 · 9H2O |
| 8.CB.50 | Kolovratite | NixZny(VO4)0.67(x+y) · nH2O |
| 8.CB.60 | Burgessite | Co2(H2O)4[AsO3(OH)]2(H2O) |
| 8.CB.65 | Cardite | Zn5.5(AsO4)2(AsO3OH)(OH)3 · 3H2O |
Fluorescence of Geminite
None
Other Information
Thermal Behaviour:
On heating, the mineral becomes anhydrous between 200°C and 250°C.
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 Geminite
mindat.org URL:
https://www.mindat.org/min-1671.html
Please feel free to link to this page.
Please feel free to link to this page.
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Mineral Dealers:
References for Geminite
Reference List:
Cooper, M. A., Hawthorne, F. C. (1995) The crystal structure of geminite, Cu2+(AsO3OH)(H2O), a heteropolyhedral sheet structure. The Canadian Mineralogist, 33 (5) 1111-1118
Plumhoff, Alexandra M., Plášil, Jakub, Dachs, Edgar, Benisek, Artur, Sejkora, Jiří, Števko, Martin, Rumsey, Mike S., Majzlan, Juraj (2020) Thermodynamic properties, crystal structure and phase relations of pushcharovskite [Cu(AsO3OH)(H2O).0.5H2O], geminite [Cu(AsO3OH)(H2O)] and liroconite [Cu2Al(AsO4)(OH)4.4H2O]. European Journal of Mineralogy, 32 (3). 285-304 doi:10.5194/ejm-32-285-2020
Localities for Geminite
Showing 11 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.
Czech Republic | |
| Hloušek et al. (2002) |
| Hloušek et al. (2002) +1 other reference | |
France | |
| [AmMin 84:197] |
| Sarp et al. (1990) +1 other reference |
Germany | |
| Lapis 1994 (10) |
Greece | |
| ... |
| Rieck et al. (2018) |
Italy | |
| Caboni et al. (2018) |
Morocco | |
| Favreau et al. (2006) |
Namibia | |
| Hawthorne et al. (2012) |
Poland | |
| Material analysed by University of ... +1 other reference |
Quick NavTopAbout GeminiteUnique IdentifiersSimilar NamesIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesCommon AssociatesStrunz-MindatFluorescence Other InformationInternet Links References Localities Locality List
Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic