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Chemical formulaOxalate(Oxalic acid) (Calcium oxalate dihydrate CaC2O4·2H2O )
ColorYellowish brown
Crystal habiteight-face bi-pyramid (typical)
Crystal systemTetragonal
Mohs Scale hardness4
LusterVitreous (Glassy)
Refractive index1.52-1.54 - DR +0.009 (B-G interval)

Weddellite (CaC2O4·2H2O) is a mineral form of calcium oxalate named for occurrences of millimeter-sized crystals found in bottom sediments of the Weddell Sea, off Antarctica. Occasionally, weddellite partially dehydrates to whewellite, forming excellent pseudomorphs of grainy whewellite after weddellite's short tetragonal dipyramids.


Structural properties

The weddelite or calcium oxalate di-hydrate crystallizes in the tetragonal system. The classic crystal shape is the eight-face bi-pyramid. In bright field microscopy, the weddelite crystals are recognized easily by their shape that reminds a mail envelope. More complex shapes of weddelite are possible. The dumbbell shape is not rare. The former has no precise angles or sides. This form is, in reality, a microcrystalline agglomerate that takes the shape of a biconcave disc. Weddelite crystals are poorly birefringent and do not show any interference pattern under polarized light.

Biological role

Weddelite crystals are usually of little clinical value. Many specimens develop weddelite crystals on standing. Together, apatite, whewellite, and weddellite are probably the most common urinary stones.

Varieties and related minerals

Natroxalate, Whewellite, Caoxite, Novgorodovaite, Oxammite, Glushinskite, Humboldtine, Minguzzite, Zhemchuzhnikovite, Stepanovite, Moolooite, Wheatleyite, Coskrenite


  • Weddellite. Weddellite: Weddellite mineral data. Retrieved on June 23, 2005.
  • Weddellite. MINERALOGY OF KIDNEY STONES. Retrieved on June 21, 2005.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Weddellite". A list of authors is available in Wikipedia.
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