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Coquimbite
A valid IMA mineral species - grandfathered
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About Coquimbite
Formula:
AlFe3(SO4)6(H2O)12 · 6H2O
Formerly given as Fe2-xAlx(SO4)3.9H2O (x ~0.5) or even Fe2(SO4)3.9H2O; redefined by Mauro et al. in 2020 (Al is essential)
Colour:
Light violet to purple, Greenish white, Bluish white, Yellowish white, Brownish white
Lustre:
Sub-Vitreous, Resinous, Waxy, Greasy
Hardness:
2½
Specific Gravity:
2.11
Crystal System:
Trigonal
Member of:
Name:
Named in 1841 by August Breithaupt for the type locality in the province of Coquimbo, Chile
Type Locality:
Visually indistinguishable from aluminocoquimbite and paracoquimbite, all structurally homeotypic.
Redefined by Mauro et al. in 2020 as a group containing variable Al/Fe ratios, increasing from paracoquimbite to coquimbite to aluminocoquimbite. There are three non-equivalent metal sites, all with octahedral coordination: the M(1) site, contains Fe and/or Al, dominated by Al in coquimbite, coordinated only by water, M(2) contains Al and/or Fe ( Fe dominates in coquimbite), exclusively coordinated by the sulfate groups, while M(3) contains only Fe, coordinated by water and sulphate groups.
As a consequence, many “coquimbite” samples may be mislabelled unless carefully analysed chemically.
Compare the visually similar 'UM1988-20-SO:FeH'.
Redefined by Mauro et al. in 2020 as a group containing variable Al/Fe ratios, increasing from paracoquimbite to coquimbite to aluminocoquimbite. There are three non-equivalent metal sites, all with octahedral coordination: the M(1) site, contains Fe and/or Al, dominated by Al in coquimbite, coordinated only by water, M(2) contains Al and/or Fe ( Fe dominates in coquimbite), exclusively coordinated by the sulfate groups, while M(3) contains only Fe, coordinated by water and sulphate groups.
As a consequence, many “coquimbite” samples may be mislabelled unless carefully analysed chemically.
Compare the visually similar 'UM1988-20-SO:FeH'.
Unique Identifiers
Mindat ID:
1126
Long-form identifier:
mindat:1:1:1126:2
IMA Classification of Coquimbite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
AlFe3+3(S6+O4)6(H2O)12·6H2O
Approval history:
redefinition code: IMA 19-F
Classification of Coquimbite
7.CB.55
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
B : With only medium-sized cations
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
B : With only medium-sized cations
Dana 7th ed.:
29.8.3.1
29.8.3.1
29 : HYDRATED ACID AND NORMAL SULFATES
8 : A2(XO4)3·H2O
29 : HYDRATED ACID AND NORMAL SULFATES
8 : A2(XO4)3·H2O
25.10.9
25 : Sulphates
10 : Sulphates of Fe alone
25 : Sulphates
10 : Sulphates of Fe alone
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 |
|---|---|---|
| Coq | 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 Coquimbite
Sub-Vitreous, Resinous, Waxy, Greasy
Transparency:
Transparent
Colour:
Light violet to purple, Greenish white, Bluish white, Yellowish white, Brownish white
Streak:
White
Hardness:
2½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Imperfect/Fair
fair/imperfect on [1011]
very poor/difficult on {1010}
fair/imperfect on [1011]
very poor/difficult on {1010}
Fracture:
Sub-Conchoidal
Density:
2.11(1) g/cm3 (Measured) 2.12 g/cm3 (Calculated)
Comment:
Dana, 7th ed. gives calculated density as 2.137.
Optical Data of Coquimbite
Type:
Uniaxial (+)
RI values:
nω = 1.539 nε = 1.548
Birefringence:
0.009
Max. Birefringence:
δ = 0.009
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:
None to Very Low
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 uniaxial interference figure - the conoscopic
(convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis
centred and vertical. The coloured rings are isochromatics, computed with the
same physics as the Michel-Lévy bar above; the dark cross is the isogyre.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
Optical Extinction:
Parallel
Pleochroism:
Non-pleochroic
Chemistry of Coquimbite
Mindat Formula:
AlFe3(SO4)6(H2O)12 · 6H2O
Formerly given as Fe2-xAlx(SO4)3.9H2O (x ~0.5) or even Fe2(SO4)3.9H2O; redefined by Mauro et al. in 2020 (Al is essential)
Formerly given as Fe2-xAlx(SO4)3.9H2O (x ~0.5) or even Fe2(SO4)3.9H2O; redefined by Mauro et al. in 2020 (Al is essential)
Element Weights:
Common Impurities:
Al
Crystallography of Coquimbite
Crystal System:
Trigonal
Class (H-M):
3m(32/m) - Hexagonal Scalenohedral
Space Group:
P31c
Cell Parameters:
a = 10.922(9) Å, c = 17.084(14) Å
Ratio:
a:c = 1 : 1.564
Unit Cell V:
1,764.92 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Short prismatic [0001] with {1010} and {1120} to pyramidal crystals {1011}. Massive, granular.
M(3) is surrounded by three oxygens of the sulfate groups and three belonging to water molecules. There are M(2)M(3)2(SO4)6(H2O)6 clusters. Sulfate groups participating in the formation of these clusters are corner-sharing. Additional 6 water groups are held only be hydrogen bonding. Interaction of Fe3(SO4)6(H2O)6 clusters via hydrogen bonds gives rise to discontinuous zig-zag chains along [001]. Further hydrogen bond interaction of these chains with isolated Al(H2O)6 octahedra produces cages containing interstitial water.
M(3) is surrounded by three oxygens of the sulfate groups and three belonging to water molecules. There are M(2)M(3)2(SO4)6(H2O)6 clusters. Sulfate groups participating in the formation of these clusters are corner-sharing. Additional 6 water groups are held only be hydrogen bonding. Interaction of Fe3(SO4)6(H2O)6 clusters via hydrogen bonds gives rise to discontinuous zig-zag chains along [001]. Further hydrogen bond interaction of these chains with isolated Al(H2O)6 octahedra produces cages containing interstitial water.
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) |
|---|---|---|---|---|---|---|---|
| 0006336 | Coquimbite | Demartin F, Castellano C, Gramaccioli C M, Campostrini I (2010) Aluminum-for-iron substitution, hydrogen bonding, and a novel structure-type in coquimbite-like minerals The Canadian Mineralogist 48 323-333 | 2010 | Alum Grotto, Vulcano, Aeolian Islands, Sicily, Italy | 0 | 293 | |
| 0006335 | Coquimbite | Demartin F, Castellano C, Gramaccioli C M, Campostrini I (2010) Aluminum-for-iron substitution, hydrogen bonding, and a novel structure-type in coquimbite-like minerals The Canadian Mineralogist 48 323-333 | 2010 | the Dexter No. 7 mine, Calf Mesa, San Rafael Swell, Utah, USA | 0 | 293 | |
| 0006334 | Coquimbite | Demartin F, Castellano C, Gramaccioli C M, Campostrini I (2010) Aluminum-for-iron substitution, hydrogen bonding, and a novel structure-type in coquimbite-like minerals The Canadian Mineralogist 48 323-333 | 2010 | La Alcaparrosa, Chile | 0 | 293 | |
| 0007144 | Coquimbite | Majzlan J, Navrotsky A, McCleskey R B, Alpers C N (2006) Thermodynamic properties and crystal structure refinement of ferricopiapite, coquimbite, rhomboclase, and Fe2(SO4)3(H2O)5 European Journal of Mineralogy 18 175-186 | 2006 | synthetic | 0 | 293 | |
| 0000211 | Coquimbite | Fang J H, Robinson P D (1970) Crystal structures and mineral chemistry of hydrated ferric sulfates. I. The crystal structure of coquimbite American Mineralogist 55 1534-1540 |  | 1970 | 0 | 293 |
CIF Raw Data - click here to close
Epitaxial Relationships of Coquimbite
Epitaxial Minerals:
| 'Paracoquimbite' | Fe4(SO4)6(H2O)12 · 6H2O |
Epitaxy Comments:
Paracoquimbite in parallel position. Lamellar intergrowths on {0001}, or as scepter-like overgrowths.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.28 Å | (80) |
| 5.47 Å | (60) |
| 4.60 Å | (60) |
| 3.64 Å | (60) |
| 3.50 Å | (50) |
| 3.36 Å | (100) |
| 2.77 Å | (50) |
| 2.76 Å | (80) |
Comments:
ICDD 44-1425
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 45a : [Sulfates, arsenates, selenates, antimonates] | |
| 47a : [Near-surface hydration of prior minerals] | |
| 47b : [Sulfates and sulfites] | |
| Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere | <0.6 |
| 50 : Coal and/or oil shale minerals | <0.36 |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 54 : Coal and other mine fire minerals (see also #51 and #56) | |
| 55 : Anthropogenic mine minerals |
Geological Setting:
Secondary weathering zone of iron sulfide deposits in arid regions. Rarely in fumaroles.
Type Occurrence of Coquimbite
Place of Conservation of Type Material:
Mining Academy, Freiberg, Germany 18558; neotype: U.S. National Museum, Washington DC, USA, catalogue number 12548 (Tierra Amarilla material; Rose, 1833; Fang and Robinson, 1970)
Synonyms of Coquimbite
White Copperas (in part)
Other Language Names for Coquimbite
Varieties of Coquimbite
| Aluminous Coquimbite | An aluminous variety of coquimbite formed as a by-product of a burning pyritic orebody. |
Relationship of Coquimbite to other Species
Member of:
Other Members of Coquimbite Group:
| Aluminocoquimbite | Al2Fe2(SO4)6(H2O)12 · 6H2O | Trig. 3m(32/m) : P31c |
| Paracoquimbite | Fe4(SO4)6(H2O)12 · 6H2O | Trig. 3 : R3 |
Common Associates
Associations Based on Photo Data:
| 82 photos of Coquimbite associated with Römerite | Fe2+Fe3+2(SO4)4 · 14H2O |
| 62 photos of Coquimbite associated with Halotrichite | Fe2+Al2(SO4)4 · 22H2O |
| 50 photos of Coquimbite associated with Copiapite | Fe2+Fe3+4(SO4)6(OH)2 · 20H2O |
| 48 photos of Coquimbite associated with Alunogen | Al2(SO4)3 · 17H2O |
| 44 photos of Coquimbite associated with Voltaite | K2Fe2+5Fe3+3Al(SO4)12 · 18H2O |
| 41 photos of Coquimbite associated with Chalcanthite | CuSO4 · 5H2O |
| 30 photos of Coquimbite associated with Goldichite | KFe(SO4)2 · 4H2O |
| 27 photos of Coquimbite associated with Krausite | KFe(SO4)2 · H2O |
| 9 photos of Coquimbite associated with Metavoltine | K2Na6Fe2+Fe3+6O2(SO4)12 · 18H2O |
| 8 photos of Coquimbite associated with Szomolnokite | FeSO4 · H2O |
Related Minerals - Strunz-mindat Grouping
| 7.CB. | Sarvodaite | Al2(SO4)3 · 5H2O |
| 7.CB.02 | Voudourisite | CdSO4 · H2O |
| 7.CB.05 | Szmikite | MnSO4 · H2O |
| 7.CB.05 | Szomolnokite | FeSO4 · H2O |
| 7.CB.05 | Cobaltkieserite | CoSO4 · H2O |
| 7.CB.05 | Dwornikite | Ni(SO4) · H2O |
| 7.CB.05 | Kieserite | MgSO4 · H2O |
| 7.CB.05 | Poitevinite | (Cu,Fe)SO4 · H2O |
| 7.CB.05 | Gunningite | ZnSO4 · H2O |
| 7.CB.07 | Sanderite | MgSO4 · 2H2O |
| 7.CB.10 | Bonattite | CuSO4 · 3H2O |
| 7.CB.12 | Belogubite | CuZn(SO4)2 · 10H2O |
| 7.CB.15 | Drobecite | CdSO4 · 4H2O |
| 7.CB.15 | Aplowite | CoSO4 · 4H2O |
| 7.CB.15 | Cranswickite | MgSO4 · 4H2O |
| 7.CB.15 | Rozenite | FeSO4 · 4H2O |
| 7.CB.15 | Starkeyite | MgSO4 · 4H2O |
| 7.CB.15 | Ilesite | Mn2+(SO4) · 4H2O |
| 7.CB.15 | Boyleite | ZnSO4 · 4H2O |
| 7.CB.20 | Siderotil | FeSO4 · 5H2O |
| 7.CB.20 | Jôkokuite | MnSO4 · 5H2O |
| 7.CB.20 | Pentahydrite | MgSO4 · 5H2O |
| 7.CB.20 | Chalcanthite | CuSO4 · 5H2O |
| 7.CB.25 | Chvaleticeite | Mn2+(H2O)6(SO4) |
| 7.CB.25 | Nickelhexahydrite | Ni2+(H2O)6(SO4) |
| 7.CB.25 | Hexahydrite | Mg(H2O)6(SO4) |
| 7.CB.25 | Bianchite | Zn(H2O)6(SO4) |
| 7.CB.25 | Moorhouseite | Co2+(H2O)6(SO4) |
| 7.CB.25 | Ferrohexahydrite | Fe2+(H2O)6(SO4) |
| 7.CB.30 | Retgersite | NiSO4 · 6H2O |
| 7.CB.35 | Zincmelanterite | Zn(H2O)6(SO4) · H2O |
| 7.CB.35 | Melanterite | Fe2+(H2O)6(SO4) · H2O |
| 7.CB.35 | Alpersite | (Mg,Cu2+)(H2O)6(SO4) · H2O |
| 7.CB.35 | Bieberite | Co2+(H2O)6(SO4) · H2O |
| 7.CB.35 | Boothite | Cu2+(H2O)6(SO4) · H2O |
| 7.CB.35 | Mallardite | Mn2+(H2O)6(SO4) · H2O |
| 7.CB.40 | Epsomite | MgSO4 · 7H2O |
| 7.CB.40 | Goslarite | ZnSO4 · 7H2O |
| 7.CB.40 | Morenosite | NiSO4 · 7H2O |
| 7.CB.45 | Meta-alunogen | Al2(SO4)3 · 12H2O |
| 7.CB.45 | Alunogen | Al2(SO4)3 · 17H2O |
| 7.CB.50 | Aluminocoquimbite | Al2Fe2(SO4)6(H2O)12 · 6H2O |
| 7.CB.50 | Lazaridisite | Cd3(SO4)3 · 8H2O |
| 7.CB.52 | Pararaisaite | CuMg[Te6+O4(OH)2] · 6H2O |
| 7.CB.55 | Paracoquimbite | Fe4(SO4)6(H2O)12 · 6H2O |
| 7.CB.55 | Rhomboclase | (H5O2)Fe3+(SO4)2 · 2H2O |
| 7.CB.55 | Raisaite | CuMg[Te6+O4(OH)2] · 6H2O |
| 7.CB.57 | 'Caichengyunite' | Fe2+3Al2(SO4)6 · 30H2O |
| 7.CB.60 | Kornelite | Fe2(SO4)3 · 7H2O |
| 7.CB.65 | Quenstedtite | Fe2(SO4)3 · 11H2O |
| 7.CB.70 | Lausenite | Fe2(SO4)3 · 5H2O |
| 7.CB.75 | Römerite | Fe2+Fe3+2(SO4)4 · 14H2O |
| 7.CB.75 | Lishizhenite | ZnFe2(SO4)4 · 14H2O |
| 7.CB.80 | Ransomite | CuFe2(SO4)4 · 6H2O |
| 7.CB.85 | Dietrichite | ZnAl2(SO4)4 · 22H2O |
| 7.CB.85 | Halotrichite | Fe2+Al2(SO4)4 · 22H2O |
| 7.CB.85 | Apjohnite | Mn2+Al2(SO4)4 · 22H2O |
| 7.CB.85 | Redingtonite | Fe2+Cr3+2(SO4)4 · 22H2O |
| 7.CB.85 | Pickeringite | MgAl2(SO4)4 · 22H2O |
| 7.CB.85 | Bílinite | Fe2+Fe3+2(SO4)4 · 22H2O |
| 7.CB.85 | Wupatkiite | Co2+Al2(SO4)4 · 22H2O |
| 7.CB.90 | Meridianiite | MgSO4 · 11H2O |
Fluorescence of Coquimbite
Not fluorescent in UV
Other Information
Notes:
Soluble in cold water and cold mineral acids; astringent taste, efforesces in dry air as a white powder; heating a water solution causes decomposition of the solution with precipitation of hydrated ferric oxide
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 Coquimbite
mindat.org URL:
https://www.mindat.org/min-1126.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
External Links:
Mineral Dealers:
Alcaparrosa Mine, Sierra Gorda, Antofagasta Province, Antofagasta, Chile