Weddellite is a rare calcium oxalate mineral typically found in sedimentary environments and sometimes associated with biological processes. It most commonly appears as small, colorless or pale yellow tetragonal bipyramidal crystals that are notable for their unique formation history in organic-rich settings.
Is this weddellite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch weddellite with a known reference. Weddellite sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, tan, white, yellowish brown, brown.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: bipyramidal crystals.
Often confused with
Weddellite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside weddellite
Minerals reported to co-occur with weddellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaC₂O₄·2H₂O
- Mohs hardness
- ~4
- Density
- 1.94 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Bipyramidal crystals
- Cleavage
- Good on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Authigenic in bottom muds and in peat sediments; in calcareous lake-bottom sediments; may be formed by reaction of calcite with oxalic acid produced by lichens
Where rockhounds find weddellite
Classic worldwide localities
- Sami Tsubota jasper mine, four km south of Biggs, Sherman Co., Oregon, USA
- Central and marginal Weddell Sea, Antarctica
- South Georgia Island, southern Atlantic Ocean
- Jingemia Cave, Toppin Hill Cave, and Petrogale Cave, near Madura, Western Australia
- Gcwihaba Cave, 280 km west of Maun, northwestern Botswana
- Tyllakh brown coal deposit, left bank of the Olenhinskii channel near its mouth, estuary of the Lena River, Bulun district, polar Sakha, Russia
Field-hunting tip
Where it forms: Authigenic in bottom muds and in peat sediments; in calcareous lake-bottom sediments; may be formed by reaction of calcite with oxalic acid produced by lichens. If you start seeing whewellite, urea, phosphammite in float, you are in the right ground. Typical habit: bipyramidal crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify weddellite?+
Where is weddellite found?+
What rocks look like weddellite?+
What minerals are found with weddellite?+
What kind of rock does weddellite form in?+
What is weddellite used for?+
Find weddellite on the map
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