Petewilliamsite is a very rare nickel arsenate mineral typically found as small, dark violet-red to dark brownish red crusts or tiny prismatic crystals. It is most often found in association with other rare arsenates in the oxidized zones of nickel-cobalt ore deposits.
Is this petewilliamsite?
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 petewilliamsite with a known reference. Petewilliamsite sits at Mohs <5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale reddish brown to purplish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark violet red, dark brownish red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates.
Often confused with
Petewilliamsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Petewilliamsite is noticeably harder (Mohs <5 vs. 1.5-2.5); luster reads vitreous on Petewilliamsite and subadamantine, pearly on cleavages, may be dull, earthy on Annabergite.
How to tell apart: Petewilliamsite is noticeably harder (Mohs <5 vs. 1.5-2.5); luster reads vitreous on Petewilliamsite and subadamantine, pearly on cleavages on Erythrite.
Often found alongside petewilliamsite
Minerals reported to co-occur with petewilliamsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ni,Co)₃(As₂O₈)
- Mohs hardness
- <5
- Density
- 4.904 g/cm³
- Colors
- Dark violet redDark brownish red
- Streak
- Pale reddish brown to purplish brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Known from one specimen; therein the product of oxidation of nickeline
Where rockhounds find petewilliamsite
Classic worldwide localities
- Johanngeorgenstadt, Saxony, Germany
Field-hunting tip
Where it forms: Known from one specimen; therein the product of oxidation of nickeline. If you start seeing xanthiosite, aerugite, paganoite in float, you are in the right ground. Typical habit: aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify petewilliamsite?+
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What rocks look like petewilliamsite?+
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Find petewilliamsite on the map
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