Weddellite

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Weddellite

General
Category	Mineral
Chemical formula	Oxalate(Oxalic acid) (Calcium oxalate dihydrate CaC₂O₄·2H₂O )
Identification
Color	Yellowish brown
Crystal habit	eight-face bi-pyramid (typical)
Crystal system	Tetragonal
Twinning	yes
Cleavage	OUI
Fracture	Conchoidal
Mohs Scale hardness	4
Luster	Vitreous (Glassy)
Refractive index	1.52-1.54 - DR +0.009 (B-G interval)
Streak	White

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.

1 Structural properties
2 Biological role
3 Varieties and related minerals
4 References

[edit] 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.

[edit] 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.

[edit] Varieties and related minerals

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