Cassidyite is a rare phosphate mineral found in oxidized nickel-rich environments. Collectors typically look for its distinctive pale green, tabular crystals often occurring in radiating clusters or thin crusts.
Is this cassidyite?
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 cassidyite with a known reference. Cassidyite sits at Mohs 3.5, 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: green, light green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular crystals, radiating aggregates, crusts.
Often confused with
Cassidyite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Roscherite is the harder of the two (Mohs 4.5 vs. 3.5); streak differs, so Cassidyite leaves white, Roscherite leaves light brown.
How to tell apart: Goyazite is the harder of the two (Mohs 4.5-5 vs. 3.5); luster reads vitreous on Cassidyite and greasy to resinous, pearly on cleavages on Goyazite.
Often found alongside cassidyite
Minerals reported to co-occur with cassidyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Ni(PO₄)₂·2H₂O
- Mohs hardness
- 3.5
- Density
- 3.1 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Tabular crystals, radiating aggregates, crusts
- Cleavage
- Good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An alteration product of a highly weathered iron-nickel meteorite, formed by alteration of schreibersite
Where rockhounds find cassidyite
Classic worldwide localities
- Wolf Creek meteorite (type locality)
Field-hunting tip
Where it forms: An alteration product of a highly weathered iron-nickel meteorite, formed by alteration of schreibersite. If you start seeing reevesite, goethite, nickelian maghemite in float, you are in the right ground. Typical habit: tabular crystals, radiating aggregates, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cassidyite?+
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Find cassidyite on the map
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