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Ca(C2O4) · (2.5-x)H2O
0 ≤ x ≤ 0.25

Previously reported as CaC2O4·2H2O and CaC2O4·(2+x)H2O
Colourless, white, ...
Named after its discovery locality, the Weddell Sea, Antarctica.
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).

Classification of Weddellite

Approved, 'Grandfathered' (first described prior to 1959)

A : Salts of organic acids
B : Oxalates

1 : Oxalates

31 : Oxalates, Citrates, Mellitates and Acetates
1 : Oxalates

Physical Properties of Weddellite

Diaphaneity (Transparency):
Colourless, white, yellowish brown to brown; colourless in transmitted light.
Hardness (Mohs):
None Observed
1.94 g/cm3 (Measured)    1.962 g/cm3 (Calculated)

Optical Data of Weddellite

Uniaxial (+)
RI values:
nω = 1.523 nε = 1.544
Max Birefringence:
δ = 0.021
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:

Chemical Properties of Weddellite

Ca(C2O4) · (2.5-x)H2O

0 ≤ x ≤ 0.25

Previously reported as CaC2O4·2H2O and CaC2O4·(2+x)H2O
IMA Formula:
CaC2O4 · 2H2O
Elements listed in formula:
Common Impurities:

Crystallography of Weddellite

Crystal System:
Class (H-M):
4/m - Dipyramidal
Space Group:
Cell Parameters:
a = 12.371 Å, c = 7.357 Å
a:c = 1 : 0.595
Unit Cell Volume:
V 1,125.93 ų (Calculated from Unit Cell)
Crystals commonly isolated, with {011}, elongated [010], terminated by {001}; commonly corroded.
Single or multiple twins possibly noted.
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Occurrences of Weddellite

Type Occurrence of Weddellite

General Appearance of Type Material:
Tiny isolated crystals
Place of Conservation of Type Material:
The Natural History Museum, London, England: #1936,975 to 1936,977.
Geological Setting of Type Material:
Bottom muds of a arctic sea.

Relationship of Weddellite to other Species

10.AB.05HumboldtineFe2+(C2O4) · 2H2O
10.AB.05LindbergiteMn2+(C2O4) · 2H2O
10.AB.10GlushinskiteMg(C2O4) · 2H2O
10.AB.15MoolooiteCu(C2O4) · 0.4H2O
10.AB.20StepanoviteNaMgFe3+(C2O4)3 · 8-9H2O
10.AB.25MinguzziteK3Fe3+(C2O4)3 · 3H2O
10.AB.30WheatleyiteNa2Cu(C2O4)2 · 2H2O
10.AB.35ZhemchuzhnikoviteNaMgAl(C2O4)3 · 8H2O
10.AB.45WhewelliteCa(C2O4) · H2O
10.AB.50CaoxiteCa(C2O4) · 3H2O
10.AB.55Oxammite(NH4)2(C2O4) · H2O
10.AB.65Coskrenite-(Ce)(Ce,Nd,La)2(C2O4)(SO4)2 · 12H2O
10.AB.70Levinsonite-(Y)(Y,Nd,La)Al(C2O4)(SO4)2 · 12H2O
10.AB.75Zugshunstite-(Ce)(Ce,Nd,La)Al(C2O4)(SO4)2 · 12H2O
10.AB.80NovgorodovaiteCa2(C2O4)Cl2 · 2H2O
31.1.1Oxammite(NH4)2(C2O4) · H2O
31.1.2MoolooiteCu(C2O4) · 0.4H2O
31.1.3WheatleyiteNa2Cu(C2O4)2 · 2H2O
31.1.4GlushinskiteMg(C2O4) · 2H2O
31.1.5WhewelliteCa(C2O4) · H2O
31.1.7HumboldtineFe2+(C2O4) · 2H2O
31.1.8StepanoviteNaMgFe3+(C2O4)3 · 8-9H2O
31.1.9ZhemchuzhnikoviteNaMgAl(C2O4)3 · 8H2O
31.1.10MinguzziteK3Fe3+(C2O4)3 · 3H2O

Other Names for Weddellite

Name in Other Languages:

Other Information

Other Information:
Dehydrates to Whewellite upon exposure to air. Insoluble in water.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Weddellite

Reference List:
Nakano (1923) Journal of Biochemistry: 2: 437.

Hammarsten (1929) Comptes rendu des trav. lab. Carlsberg: 17: 1.

Bannister, F.A., Hey, M.H. (1936) Report on some crystalline components of the Weddell Sea deposits. Discovery Reports: 13: 60-69. (as hydrated calcium oxalate).

Frondel, C., Prien, E.L. (1942) Carbonate-apatite and Hydroxyl-apatite in urinary calculi. Science: 95: 431-431.

Lecompte, Pobeguin, Wyart (1943) Rendus de l’Académie des sciences de Paris: 216: 808.

Pobeguin (1943) rendu de l’Académie des sciences de Paris: 216: 500.

Prien and Frondel (1947): Journal of Urology: 57: 949 (includes study of urinary calculi).

Palache, C., Berman, H., Frondel, C. (1951) The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 1101-1102.

Sterling, C. (1965) Crystal-structure analysis of weddellite, CaC2O4·(2+x)H2O. Acta Crystallographica: 18: 917-921.

Hutton, C.O., Taft, W.H. (1965) Weddellite in Modern Sediments, Florida. Mineralogical Magazine: 34: 256-265.

Tazzoli, V., Domeneghetti, C. (1980) The crystal structures of whewellite and weddellite: re-examination and comparison. American Mineralogist: 65: 327-334.

Mandarino, J.A. (1983) Weddellite from Lutterworth Township, Haliburton County, Ontario. The Canadian Mineralogist: 21: 509-511.

Mandarino, J.A., Witt, N.V. (1983) Weddellite from Biggs, Oregon, U.S.A.. The Canadian Mineralogist: 21: 503-508.

Van de Vijver, B., Vochten, R., Geys, J., Verbruggen, C., Beyens, L. (1997) Mineralogical observations of weddellite from South Georgia, Subantarctica. Neues Jahrb. Mineral., Monatsh.: 193–202.

Burford, E.P., Kierans, M., Gadd, G.M. (2003) Geomycology: fungi in mineral substrata. Mycologist: 17(3): 98-107; DOI: 10.1017/S0269915X03003112.

Frost, R.L., Weier, M.L. (2003) Raman spectroscopy of natural oxalates at 298 and 77 K. Journal of Raman Spectroscopy: 34: 776-785.

Frost, R.L., Weier, M.L. (2003) Thermal treatment of weddellite--a Raman and infrared emission spectroscopic study. Thermochimica Acta: 406: 221-232.

Hernanz, A., Gavira-Vallejo, J.M., Ruiz-Lopez, J.F. (2007) Calcium oxalates and prehistoric paintings. The usefulness of these biominerals. Journal of Optoelectronics and Advanced Materials: 9: 512-521.

Echigo, T., Kimata, M. (2010) Crystal chemistry and genesis of organic minerals: A review of oxalate and polycyclic aromatic hydrocarbon minerals. The Canadian Mineralogist: 48: 1329-1358.

Izatulina, A., Gurzhiy, V., Frank-Kamenetskaya, O. (2014) Weddellite from renal stones: Structure refinement and dependence of crystal chemical features on H2O content. American Mineralogist: 99: 2-7.

Conti, C., Casati, M., Colombo, C., Possenti, E., Realini, M., Gatta, G.D., Merlini, M., Brambilla, L., Zerbi, G. (2015) Synthesis of calcium oxalate trihydrate: New data by vibrational spectroscopy and synchrotron X-ray diffraction. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy: 150: 721–730.

Sturm, E.V., Frank-Kamenetskaya, O., Vlasov, D., Zelenskaya, M., Sazanova, K., Rusakov, A., Kniep, R. (2015) Crystallization of calcium oxalate hydrates by interaction of calcite marble with fungus aspergillus niger. American Mineralogist: 100: 2559-2565.

Mills, S.J., Christy, A.G. (2016) The Great Barrier Reef Expedition 1928–29: The crystal structure and occurrence of weddellite, ideally CaC2O4·2.5H2O, from the Low Isles, Queensland. Mineralogical Magazine: 80: 399-406.

Internet Links for Weddellite URL:
Please feel free to link to this page.

Localities for Weddellite

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
(TL) indicates type locality for a valid mineral species. (FRL) indicates first recorded locality for everything else. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
Antarctica (TL)
  • Western Antarctica
Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 1102.
  • Western Australia
    • Dundas Shire
      • Madura Roadhouse
Mineralogical Magazine (1977): 41: 33-35.
    • Laverton Shire
      • Lake Rason
Mineralogical Magazine (1973): 39: 346-348.
    • Moora Shire
Bridge, P.J., Pryce, M.W., Clarke, R.M., and Costello, M.B. (1978): Sampleite from Jingemia Cave, Western Australia. Mineralogical Magazine 42, 369-371.
  • Salzburg
    • Hohe Tauern
      • Gastein valley
        • Siglitz - Bockhart area
Kolitsch, U. (2015): 1932) Weddelit vom Bockhartsee im Gasteiner Tal, Salzburg. P. 238 in Niedermayr, G. et al. (2015): Neue Mineralfunde aus Österreich LXIV. Carinthia II, 205./125., 207-280.
  • North-West District
    • Ngamiland West District
Handbook of Mineralogy - Anthony, Bideaux, Bladh, Nichols
  • Sofiya Oblast (Sofia Oblast)
J. Mincheva-Stefanova & I. Kostov (1994): Weddellite - a mineral new to Bulgaria. Comptes Rendus de l'Académie Bulgare des Sciences, 47, 69-72.
  • Nunavut
    • Ellesmere Island
Gault, C. D. (1986): Weddellite: a new occurrence. Mineralogical Magazine, 50, 738-739.
  • Ontario
    • Haliburton Co.
      • Lutterworth Township
Mandarino, A. (1983): Weddellite from Lutterworth Township, Haliburton County, Ontario. Canadian Mineralogist, 21, 509-511
Mandarino, J.A. (1983) Weddellite from Lutterworth Township, Haliburton County, Ontario. Canadian Mineralogist, Vol.21, p509-511
  • Inner Mongolia Autonomous Region
    • Xilin Gol League (Xilinguole Prefecture)
      • Xilinhot Co. (Xilinhaote Co.)
        • Shengli coal field
Qi Zhang, Huawen Qi, Ruizhong Hu, Xiaofei Wang (2008): Acta Mineralogica Sinica 28(4), 426-438
  • Baden-Württemberg
    • Black Forest
      • St Ulrich
Walenta, K. (2003): Oxalatmineralien aus dem Schwarzwald. Erzgräber 17, 9-16. (in German)
      • Waldshut
        • Detzeln
Hess, E., Graeser, S. & Gabriel, W. (2011): Das Porphyrwerk Detzeln im Steinatal und seine Mineralien. Lapis 36 (4), 25-35; 54.
      • Wolfach
        • Oberwolfach
          • Frohnbach valley
K. Walenta: "Die Mineralien des Schwarzwaldes", Weise (Munich), 1992
  • Northern District (HaZafon District)
    • Northern Jordan Valley
Cowgill, U.M. (1989): A naturally occurring alpha magnesium oxalate dihydrate from the northern Jordan Valley (Israel). Mineralogical Magazine: 53: 505-507
  • Emilia-Romagna
    • Modena Province
Dondi, M. & Puggioli, G. (1990): Minerali organici, 1 parte. Rivista Mineralogica Italiana, 4/1990, 189-206.
  • Liguria
    • La Spezia Province
      • Vara Valley
        • Borghetto Vara
Del Magro, S., Michelini, A., Giorgi, A. (2000): La weddellite di Cerchiara (La Spezia). Rivista Mineralogica Italianha, 1/2000, 37
Kolitsch, U., Lackner, E., Ciriotti, M.E. (2008): Lindbergite: primo ritrovamento italiano a Molinello. Addendum-corrigendum. Micro (UK Report), 2/2008, 77-78
    • Lucca Province
      • Apuan Alps
        • Stazzema
- Batoni, M. & Ceccantini, L. (2004): La miniera di Levigliani, Lucca, Toscana. Micro (località), 2/2004, 41-54. - Batoni, M. & Ceccantini, L. (2007): Errata corrige: Levigliani. Micro (località), 1/2007, 179
      • Massaciuccoli
        • Monte Niquila
del Magro, S. (2009): Weddellit vom Monte Niquila, Lucca, Italien. Lapis 34 (3), 7.
  • Veneto
    • Venice Province
      • Venice
M. Del Monte and C. Sabbioni (1983): Weddellite on limestone in the Venice environment. Environmental Science and Technology, 17, 518-522.
  • Eastern-Siberian Region
    • Sakha Republic (Saha Republic; Yakutia)
      • Polar Yakutia
        • Bulun District
          • Lena River Basin
Pekov, I. (1998) Minerals First discovered on the territory of the former Soviet Union 369p. Ocean Pictures, Moscow
Pekov, I. (1998) Minerals First discovered on the territory of the former Soviet Union 369p. Ocean Pictures, Moscow
  • Far-Eastern Region
    • Primorskiy Kray
      • Kavalerovo Mining District
        • Dal'negorsk (Dalnegorsk; Tetyukhe; Tjetjuche; Tetjuche)
Min Rec vol 32, pp 7-30 (2001)
  • England
    • Derbyshire
      • Ashover
        • Milltown
[MinRec 21:492]
Rust S.A. (1983): Weddellite - a new British mineral species from Derbyshire. Mineral Realm 3, 22.; Rust, S. Seltene Mineralien aus dem Steinbruch Milltown bei Ashover LAPIS Mineralienmagazin 1994, 12, p.13-17, 58; Ford, T., A. Sarjeant & M. Smith (1993): The minerals of the Peak district of Derbyshire. UK Jour. Mines & Minerals 13, 16-55.
  • Arizona
Garvie, L. A. (2003). Decay-induced biomineralization of the saguaro cactus (Carnegiea gigantea). American Mineralogist, 88(11-12), 1879-1888.
Miklancic collection, 13/50
  • Florida
G. M. Griffin, R. K. Sawyer & S. R. Melkote (1984): Weddellite occurrence in peats and other organic-rich sediments of Florida. Journal of Sedimentary Petrology, 54, 861-868.
G. M. Griffin, R. K. Sawyer & S. R. Melkote (1984): Weddellite occurrence in peats and other organic-rich sediments of Florida. Journal of Sedimentary Petrology, 54, 861-868.
  • Oregon
    • Sherman Co.
J. A. Mandarino & N. V. Witt (1983): Weddellite from Biggs, Oregon, U.S.A. Canadian Mineralogist, 21, 503-508.
  • Virginia
    • Amelia Co.
      • Winterham
Rocks & Minerals 79:4 p 256
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