Isoclasite is a rare phosphate mineral typically found as delicate acicular or fibrous crusts in hydrothermal metal deposits. Collectors value it for its tendency to form attractive radiating spray habits that require magnification to fully appreciate.
Is this isoclasite?
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 isoclasite with a known reference. Isoclasite sits at Mohs 1.5, 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 to pearly.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous.
Often confused with
Isoclasite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside isoclasite
Minerals reported to co-occur with isoclasite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂PO₄(OH)·2H₂O
- Mohs hardness
- 1.5
- Density
- 2.92 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous
- Cleavage
- Distinct on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Found with chalcedony and dolomite
Where rockhounds find isoclasite
Classic worldwide localities
- Jachymov, Zapadocesky Kraj, Bohemia, Czech Republic (type locality)
Field-hunting tip
Where it forms: Found with chalcedony and dolomite. If you start seeing arsenopyrite, pharmacosiderite, skutterudite in float, you are in the right ground. Typical habit: fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify isoclasite?+
Where is isoclasite found?+
What rocks look like isoclasite?+
What minerals are found with isoclasite?+
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What is isoclasite used for?+
Find isoclasite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
