Whewellite is a rare calcium oxalate mineral typically found in coal seams or hydrothermal ore veins. It is highly valued by collectors for its transparent, well-defined monoclinic crystals which often exhibit complex twinning.
Is this whewellite?
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 whewellite with a known reference. Whewellite sits at Mohs 2.5-3, 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, pearly on {010} and some cleavages.
- 4Match the color rangeCompare against the expected color range: colorless, brownish, gray, yellow, yellow brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular to prismatic crystals, often twinned.
Often confused with
Whewellite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Weddellite is the harder of the two (Mohs ~4 vs. 2.5-3).
How to tell apart: Luster reads vitreous, pearly on {010} and some cleavages on Whewellite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
Often found alongside whewellite
Minerals reported to co-occur with whewellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(C₂O₄)·H₂O
- Mohs hardness
- 2.5-3
- Density
- 2.21-2.23 g/cm³
- Streak
- White
- Luster
- Vitreous, pearly on {010} and some cleavages
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular to prismatic crystals, often twinned
- Cleavage
- Good on {101}, imperfect on {010}, indistinct on {001}, {110}
- Fluorescence
- Often exhibits white, yellow, or blue fluorescence under UV light
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Of uncommon occurrence as a low-temperature primary hydrothermal mineral in carbonate-sulfide veins, geodes, or septarian nodules
Where rockhounds find whewellite
1 mapped spotsClassic worldwide localities
- Elm Springs, Meade Co., South Dakota, USA
- Biggs, Sherman Co., Oregon, USA
- Radon mine, near Moab, San Juan Co., Utah, USA
- Huron River, about 2 km west of Milan, Erie Co., Ohio, USA
- Saxony, at Freital-Burgk, near Dresden, Germany
- Himmelsfürst mine, Erbisdorf, near Freiberg, Germany
Field-hunting tip
Where it forms: Of uncommon occurrence as a low-temperature primary hydrothermal mineral in carbonate-sulfide veins, geodes, or septarian nodules. If you start seeing calcite, barite, sphalerite in float, you are in the right ground. Typical habit: tabular to prismatic crystals, often twinned. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in South Dakota. Start trip planning there.
Common questions
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Find whewellite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
