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Mcguinnessite
A valid IMA mineral species
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About Mcguinnessite
Albert L. "Al" McGuinness
Formula:
(Mg,Cu)2(CO3)(OH)2
Colour:
Light blue-green, Cu-rich cores slightly darker blue, Mg-rich rims very pale blue-green to nearly white
Lustre:
Vitreous, Silky
Hardness:
2½
Specific Gravity:
3.02 - 3.22
Crystal System:
Monoclinic
Member of:
Name:
Named in honor of Albert Leo "Al" McGuinness (17 August 17, 1926, Oakland, California, USA - 29 September 1990, Oregon, USA), mining engineer and mineral collector and dealer. He collected and discovered the mineral.
Rosasite Group.
A Ni-rich mcguinnessite approaching the composition of a hypothetical end-member NiMg(CO3)(OH)2 has been described by Féher et al. (2010).
A Ni-rich mcguinnessite approaching the composition of a hypothetical end-member NiMg(CO3)(OH)2 has been described by Féher et al. (2010).
Unique Identifiers
Mindat ID:
2615
Long-form identifier:
mindat:1:1:2615:0
IMA Classification of Mcguinnessite
Approved
IMA Formula:
Cu2+MgCO3(OH)2
Approval year:
1977
First published:
1981
Classification of Mcguinnessite
5.BA.10
5 : CARBONATES (NITRATES)
B : Carbonates with additional anions, without H2O
A : With Cu, Co, Ni, Zn, Mg, Mn
5 : CARBONATES (NITRATES)
B : Carbonates with additional anions, without H2O
A : With Cu, Co, Ni, Zn, Mg, Mn
16a.3.1.4
16a : ANHYDROUS CARBONATES CONTAINING HYDROXYL OR HALOGEN
3 : (AB)2(XO3)Zq
16a : ANHYDROUS CARBONATES CONTAINING HYDROXYL OR HALOGEN
3 : (AB)2(XO3)Zq
11.3.11
11 : Carbonates
3 : Carbonates of Mg
11 : Carbonates
3 : Carbonates of Mg
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 |
|---|---|---|
| Mgu | 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 Mcguinnessite
Vitreous, Silky
Transparency:
Translucent
Colour:
Light blue-green, Cu-rich cores slightly darker blue, Mg-rich rims very pale blue-green to nearly white
Streak:
White
Hardness:
2½ on Mohs scale
Tenacity:
Brittle
Comment:
Fracture: Even
Density:
3.02 - 3.22 g/cm3 (Measured) 3.117 g/cm3 (Calculated)
Comment:
Calculated value is for Mg/Cu = 1.17
Optical Data of Mcguinnessite
Type:
Biaxial (-)
RI values:
nα = 1.596 - 1.602 nβ = 1.724 - 1.73 nγ = 1.724 - 1.732
Max. Birefringence:
δ = 0.128 - 0.130
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 (10°) 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 (10°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Dispersion:
r < v weak
Pleochroism:
Weak
Comments:
Z,Y (light bluish green); X (very pale green)
Chemistry of Mcguinnessite
Mindat Formula:
(Mg,Cu)2(CO3)(OH)2
Element Weights:
Chemical Analysis
Oxide wt%:
| 1 | |
|---|---|
| CuO | 60.68 % |
| MgO | 33.01 % |
| SiO2 | 6.30 % |
| Total: | 99.99 % |
Sample references:
| ID | Locality | Reference | Notes |
|---|---|---|---|
| 1 | Correc d'en Llinassos, Oms, Céret, Pyrénées-Orientales, Occitanie, France | SEM-EDS uncoated of globular blue-green aggregates. |
Crystallography of Mcguinnessite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Cell Parameters:
a = 9.398(2) Å, b = 12.011(2) Å, c = 3.379(2) Å
β = 93.28(5)°
β = 93.28(5)°
Ratio:
a:b:c = 0.782 : 1 : 0.281
Unit Cell V:
380.79 ų (Calculated from Unit Cell)
Z:
4
Comment:
May be triclinic. Space Group: P2/a or P21/a
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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2x2x2 | 3x3x3 | 4x4x4
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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) |
|---|---|---|---|---|---|---|---|
| 0011133 | Mcguinnessite | Perchiazzi N (2006) Crystal structure determination and Rietveld refinement of rosasite and mcguinnessite Zeitschrift fur Kristallographie Supplement 23 505-510 | 2006 | Red Mountain, California, USA | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 6.015 Å | (100) |
| 5.054 Å | (16) |
| 3.694 Å | (67) |
| 3.002 Å | (12) |
| 2.530 Å | (25) |
| 2.326 Å | (15) |
| 2.139 Å | (23) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 3b: Earth’s earliest hydrosphere | >4.45 |
| 13 : Hadean serpentinization | |
| Stage 5: Initiation of plate tectonics | <3.5-2.5 |
| 40 : Regional metamorphism (greenschist, amphibolite, granulite facies) |
Type Occurrence of Mcguinnessite
General Appearance of Type Material:
Spherules on joint and vein surfaces.
Place of Conservation of Type Material:
U.S. National Museum, Washington, D.C., USA (NMNH #147169).
Mineralogical Collection of the University P. and M. Curie, Paris, France.
Mineralogical Collection of the University P. and M. Curie, Paris, France.
Geological Setting of Type Material:
Rodingitized metagabbro dikes in a serpentinized peridotite
Associated Minerals at Type Locality:
Sierra Magnesite Mine, Gabbs, Gabbs Mining District, Nye County, Nevada, USA