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Weddellite
A valid IMA mineral species - grandfathered
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About Weddellite
The Weddell Sea
Formula:
Ca(C2O4) · (2.5-x)H2O
0 ≤ x ≤ 0.25
Previously reported as CaC2O4·2H2O and CaC2O4·(2+x)H2O
Previously reported as CaC2O4·2H2O and CaC2O4·(2+x)H2O
Colour:
Colourless, white, yellowish brown to brown; colourless in transmitted light.
Lustre:
Vitreous, Silky, Dull
Hardness:
4
Specific Gravity:
1.94
Crystal System:
Tetragonal
Name:
Named after its discovery locality, the Weddell Sea, Antarctica. The first natural and non-biologically produced material was described by Bannister and Hey (1936), but they did not name it. Frondel and Prien (1942) used the name weddellite for the first time but gave no data.
Type Locality:
Authigenic in bottom sediments and peat; in calcareous lacustrine sediments; also formed by reaction of calcite with oxalic acid derived from lichens; also from solutions derived from bat guano. Known as component of human urinary stones. May also be produced by fungi (e.g., Burford et al., 2003; compare 'Unnamed (Pb Oxalate Dihydrate)'); as such is found in soils and leaf litter; also formed by lichens liivng on basalts, serpentinites, Cu-bearing rocks, gabbroes, dolerites, andesites, volcanic clasts; examples of organisms producing it are numerous, with Acarospora rugulosa, Geastrum spp. and Lecidea lactea, to mention some.
NOTE: Cleaning of any specimens with oxalic acid will lead to crystallisation of whewellite or weddellite if Ca-bearing soluble species are present on the specimen.
Contains zeolitic water. May occur in coral reefs. These observations, as well as confirmation of an additional water site, and the current formula, are taken from Mills & Christy (2016).
NOTE: Cleaning of any specimens with oxalic acid will lead to crystallisation of whewellite or weddellite if Ca-bearing soluble species are present on the specimen.
Contains zeolitic water. May occur in coral reefs. These observations, as well as confirmation of an additional water site, and the current formula, are taken from Mills & Christy (2016).
Unique Identifiers
Mindat ID:
4254
Long-form identifier:
mindat:1:1:4254:9
Similar Names
| Wadalite | A valid IMA mineral species | (Ca,Mg)6(Al,Fe3+)4((Si,Al)O4)3O4Cl3 |
| Woodallite | A valid IMA mineral species | Mg6Cr2(OH)16Cl2 · 4H2O |
IMA Classification of Weddellite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Ca(C2)6+O4·2H2O
First published:
1936
Classification of Weddellite
10.AB.40
10 : ORGANIC COMPOUNDS
A : Salts of organic acids
B : Oxalates
10 : ORGANIC COMPOUNDS
A : Salts of organic acids
B : Oxalates
50.1.2.1
50 : ORGANIC COMPOUNDS
1 : Oxalates
50 : ORGANIC COMPOUNDS
1 : Oxalates
31.1.6
31 : Oxalates, Citrates, Mellitates and Acetates
1 : Oxalates
31 : Oxalates, Citrates, Mellitates and Acetates
1 : Oxalates
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 |
|---|---|---|
| Wed | 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 Weddellite
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Weddellite
Vitreous, Silky, Dull
Transparency:
Transparent
Colour:
Colourless, white, yellowish brown to brown; colourless in transmitted light.
Streak:
White
Hardness:
4 on Mohs scale
Cleavage:
None Observed
Mandarino and Witt (1983) report a good {010} cleavage, unlike other descriptions.
Mandarino and Witt (1983) report a good {010} cleavage, unlike other descriptions.
Fracture:
Sub-Conchoidal
Density:
1.94 g/cm3 (Measured) 1.962 g/cm3 (Calculated)
Optical Data of Weddellite
Type:
Uniaxial (+)
RI values:
nω = 1.523 nε = 1.544
Max. Birefringence:
δ = 0.021
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.
Chemistry of Weddellite
Mindat Formula:
Ca(C2O4) · (2.5-x)H2O
0 ≤ x ≤ 0.25
Previously reported as CaC2O4·2H2O and CaC2O4·(2+x)H2O
0 ≤ x ≤ 0.25
Previously reported as CaC2O4·2H2O and CaC2O4·(2+x)H2O
Element Weights:
| Element | % weight |
|---|---|
Milltown Quarry, Milltown, Ashover, North East Derbyshire District, Derbyshire, England, UK