Whitecapsite is a rare hydrated iron arsenite mineral originally discovered at the White Caps Mine in Nevada. It typically forms as small, bright yellow transparent crystals or thin crusts associated with arsenic-rich sulfide deposits.
Is this whitecapsite?
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 whitecapsite with a known reference. Whitecapsite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Whitecapsite leaves a pale yellow streak.
- 3Read the lusterHold the specimen under a strong light. Whitecapsite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellow-orange.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, crystalline crusts.
Often confused with
Whitecapsite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Whitecapsite leaves pale yellow, Pharmacosiderite leaves white; luster reads vitreous on Whitecapsite and adamantine on Pharmacosiderite.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. 2); streak differs — Whitecapsite leaves pale yellow, Scorodite leaves white; luster reads vitreous on Whitecapsite and vitreous to sub-adamantine on Scorodite.
Often found alongside whitecapsite
Minerals reported to co-occur with whitecapsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- H₄Fe₂³⁺(AsO₃)₄·4H₂O
- Mohs hardness
- 2
- Density
- 2.16 g/cm³
- Colors
- Streak
- Pale Yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Crystalline Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Sedimentary Rocks
- Typical price
- $50-300 per specimen
Where rockhounds find whitecapsite
Classic worldwide localities
- White Caps Mine, Manhattan, Nevada, USA
Field-hunting tip
Look in hydrothermal veins in sedimentary rocks country — that is the host setting where whitecapsite typically forms. If you start seeing arsenopyrite, realgar, orpiment in float, you are in the right ground. Field specimens usually show a tabular crystals, crystalline crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find whitecapsite on the map
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