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Sewardite
A valid IMA mineral species
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About Sewardite
Terry M. Seward
Formula:
CaFe3+2(AsO4)2(OH)2
Colour:
Dark red to light orange
Lustre:
Vitreous
Hardness:
3½
Specific Gravity:
4.156 (Calculated)
Crystal System:
Orthorhombic
Member of:
Name:
Named in honour of Terry Maxwell Seward (7 December 1940, Toronto, Ontario, Canada - 24 December 2022), Canadian geochemist, Professor of Geochemistry, Institut für Mineralogie und Petrographie, ETH (Swiss Federal Institute of Technology), Zürich, Switzerland. Seward’s research focuses on the chemistry of fluids on and in the earth’s crust, including low temperature aqueous systems, metal speciation, dispersion of heavy metals connected with toxic waste disposal and sea-floor hydrothermal systems. He collected the type material 20 years before the description was published.
Unique Identifiers
Mindat ID:
11128
Long-form identifier:
mindat:1:1:11128:7
IMA Classification of Sewardite
Classification of Sewardite
8.BH.30
8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H2O
H : With medium-sized and large cations, (OH,etc.):RO4 = 1:1
8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H2O
H : With medium-sized and large cations, (OH,etc.):RO4 = 1:1
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 |
|---|---|---|
| Sew | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Pronunciation of Sewardite
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Sewardite
Vitreous
Transparency:
Transparent, Translucent
Colour:
Dark red to light orange
Streak:
Reddish-brown
Hardness:
3½ on Mohs scale
Tenacity:
Brittle
Fracture:
Irregular/Uneven, Splintery
Density:
4.156 g/cm3 (Calculated)
Optical Data of Sewardite
Bireflectance:
Very weak.
Reflectivity:
| Wavelength | R1 (%) | R2 (%) |
|---|---|---|
| 400nm | 10.50% | 11.12% |
| 420nm | 10.43% | 11.05% |
| 440nm | 10.32% | 10.92% |
| 460nm | 10.12% | 10.71% |
| 470nm | 10.04% | 10.60% |
| 480nm | 9.96% | 10.49% |
| 500nm | 9.78% | 10.37% |
| 520nm | 9.69% | 10.18% |
| 540nm | 9.53% | 10.07% |
| 546nm | 9.49% | 10.06% |
| 560nm | 9.40% | 10.02% |
| 580nm | 9.30% | 9.98% |
| 589nm | 9.27% | 9.95% |
| 600nm | 9.24% | 9.92% |
| 620nm | 9.15% | 9.80% |
| 640nm | 8.99% | 9.66% |
| 650nm | 8.80% | 9.49% |
| 660nm | 8.60% | 9.37% |
| 680nm | 7.89% | 8.87% |
| 700nm | 7.25% | 8.30% |
Graph shows reflectance levels at different wavelengths (in nm). Peak reflectance is 11.12%.
R1 shown in black, R2 shown in red
Colour in reflected light:
Light bluish grey.
Internal Reflections:
Ubiquitous, very bright pink to red.
Pleochroism:
Non-pleochroic
Chemistry of Sewardite
Mindat Formula:
CaFe3+2(AsO4)2(OH)2
Element Weights:
Crystallography of Sewardite
Crystal System:
Orthorhombic
Class (H-M):
mmm(2/m2/m2/m) - Dipyramidal
Space Group:
Cccm
Cell Parameters:
a = 16.461 Å, b = 7.434 Å, c = 12.131 Å
Ratio:
a:b:c = 2.214 : 1 : 1.632
Unit Cell V:
1,484.48 ų (Calculated from Unit Cell)
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) |
|---|---|---|---|---|---|---|---|
| 0005788 | Sewardite | Roberts A C, Cooper M A, Hawthorne F C, Criddle A J, Stirling J A R (2002) Sewardite, CaFe2(AsO4)2(OH)2, the Ca-analogue of carminite, from Tsumeb, Namibia: Description and crystal structure The Canadian Mineralogist 40 1191-1198 |  | 2002 | Tsumeb, Namibia | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 4.874 Å | (90) |
| 3.473 Å | (50) |
| 3.389 Å | (60) |
| 3.167 Å | (100) |
| 3.015 Å | (50) |
| 2.988 Å | (50) |
| 2.919 Å | (70) |
| 2.503 Å | (90) |
| 1.775 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] |
Type Occurrence of Sewardite
General Appearance of Type Material:
Platy to compact anhedral to subhedral masses, up to 0.3 mm in maximum size.
Place of Conservation of Type Material:
Systematic Reference Series of the National Mineral Collection at the Geological Survey of Canada, Ottawa, Ontario, 68095.
The Natural History Museum, London, Great Britain, BM 2001.36.
The Natural History Museum, London, Great Britain, BM 2001.36.
Associated Minerals at Type Locality:
Ojuela Mine, Mapimí, Mapimí Municipality, Durango, Mexico