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Paracoquimbite
A valid IMA mineral species - grandfathered
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About Paracoquimbite
Formula:
Fe4(SO4)6(H2O)12 · 6H2O
Formerly given as Fe2(SO4)3.9H2O; changed to better address its homeotypic relation to coquimbite. The current formula is just a multiplication of the former one.
Colour:
Pale violet
Lustre:
Vitreous
Hardness:
2½
Specific Gravity:
2.11
Crystal System:
Trigonal
Member of:
Name:
From the Greek "para" for near and its relation to Coquimbite.
Note: Al is not essential in paracoquimbite (but is essential in coquimbite), as derived from the IMA redefinition.
Unique Identifiers
Mindat ID:
3084
Long-form identifier:
mindat:1:1:3084:3
Similar Names
| Paracoquimbite (of Klvana) | A synonym of Slavíkite |
IMA Classification of Paracoquimbite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Fe3+4(S6+O4)6(H2O)12·6H2O
Approval history:
redefinition code: IMA-19F
Classification of Paracoquimbite
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
29.8.4.1
29 : HYDRATED ACID AND NORMAL SULFATES
8 : A2(XO4)3·H2O
29 : HYDRATED ACID AND NORMAL SULFATES
8 : A2(XO4)3·H2O
25.10.10
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 |
|---|---|---|
| Pcoq | 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 Paracoquimbite
Vitreous
Transparency:
Transparent
Colour:
Pale violet
Hardness:
2½ on Mohs scale
Cleavage:
Imperfect/Fair
On {0112} and {10
14}, imperfect.
On {0112} and {10
14}, imperfect.
Density:
2.11(1) g/cm3 (Measured) 2.115 g/cm3 (Calculated)
Optical Data of Paracoquimbite
Type:
Uniaxial (+)
RI values:
nω = 1.55(2) nε = 1.555(2)
Max. Birefringence:
δ = 0.005
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:
Low (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 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.
Chemistry of Paracoquimbite
Mindat Formula:
Fe4(SO4)6(H2O)12 · 6H2O
Formerly given as Fe2(SO4)3.9H2O; changed to better address its homeotypic relation to coquimbite. The current formula is just a multiplication of the former one.
Formerly given as Fe2(SO4)3.9H2O; changed to better address its homeotypic relation to coquimbite. The current formula is just a multiplication of the former one.
Element Weights:
Elements listed:
Crystallography of Paracoquimbite
Crystal System:
Trigonal
Class (H-M):
3 - Rhombohedral
Space Group:
R3
Cell Parameters:
a = 10.926(9) Å, c = 51.3(21) Å
Ratio:
a:c = 1 : 4.695
Unit Cell V:
5,303.60 ų (Calculated from Unit Cell)
Z:
12
Morphology:
Crystals rhombohedral, frequently with large {0112}; also equant, pseudo-cubic, with large {0001} and {0112}, or prismatic [0001]. massive, granular.
Twinning:
On {0001}, common.
Crystal Structure
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Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
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) |
|---|---|---|---|---|---|---|---|
| 0000261 | Paracoquimbite | Robinson P D, Fang J H (1971) Crystal structures and mineral chemistry of hydrated ferric sulphates: II. The crystal structure of paracoquimbite American Mineralogist 56 1567-1572 |  | 1971 | 0 | 293 |
CIF Raw Data - click here to close
Epitaxial Relationships of Paracoquimbite
Epitaxial Minerals:
| 'Coquimbite' | AlFe3(SO4)6(H2O)12 · 6H2O |
Epitaxy Comments:
Coquimbite in parallel position; contact surface {0001}. As scepter-like overgrowths.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.88 Å | (100) |
| 8.55 Å | (20) |
| 7.62 Å | (39) |
| 5.465 Å | (29) |
| 4.713 Å | (16) |
| 4.605 Å | (29) |
| 3.367 Å | (33) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 46 : Near-surface hydrothermal alteration of minerals (see also #22) | |
| 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 |
Geological Setting:
Oxidation zone in pyrite deposits - especially in arid regions.
Type Occurrence of Paracoquimbite
Other Language Names for Paracoquimbite
Dutch:Paracoquimbiet
German:Paracoquimbit
Russian:Паракокимбит
Simplified Chinese:副针绿矾
Spanish:Paracoquimbita
Relationship of Paracoquimbite to other Species
Member of:
Other Members of Coquimbite Group:
| Aluminocoquimbite | Al2Fe2(SO4)6(H2O)12 · 6H2O | Trig. 3m(32/m) : P31c |
| Coquimbite | AlFe3(SO4)6(H2O)12 · 6H2O | Trig. 3m(32/m) : P31c |
Common Associates
Associations Based on Photo Data:
| 5 photos of Paracoquimbite associated with Metavoltine | K2Na6Fe2+Fe3+6O2(SO4)12 · 18H2O |
| 5 photos of Paracoquimbite associated with Coquimbite | AlFe3(SO4)6(H2O)12 · 6H2O |
| 2 photos of Paracoquimbite associated with Pickeringite | MgAl2(SO4)4 · 22H2O |
| 1 photo of Paracoquimbite associated with Copiapite | Fe2+Fe3+4(SO4)6(OH)2 · 20H2O |
| 1 photo of Paracoquimbite associated with Fluorite | CaF2 |
| 1 photo of Paracoquimbite associated with Aluminocopiapite | Al2/3Fe3+4(SO4)6(OH)2 · 20H2O |
| 1 photo of Paracoquimbite associated with Jarosite | KFe3+3(SO4)2(OH)6 |
| 1 photo of Paracoquimbite associated with Kornelite | Fe2(SO4)3 · 7H2O |
| 1 photo of Paracoquimbite associated with Römerite | Fe2+Fe3+2(SO4)4 · 14H2O |
| 1 photo of Paracoquimbite associated with Lausenite | Fe2(SO4)3 · 5H2O |
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 |
Alcaparrosa Mine, Sierra Gorda, Antofagasta Province, Antofagasta, Chile