Pararobertsite is a rare phosphate mineral typically found as microcrystalline crusts or powdery aggregates in granite pegmatites. It is often visually indistinguishable from its polymorph, robertsite, and usually requires X-ray diffraction for definitive identification.
Is this pararobertsite?
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 pararobertsite with a known reference. Pararobertsite 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. Streak: brownish red.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: bronze, yellow, dark red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: microcrystalline aggregates, crusts, powdery.
Often confused with
Pararobertsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Robertsite is the harder of the two (Mohs 3.5 vs. 2); streak differs, so Pararobertsite leaves brownish red, Robertsite leaves chocolate-brown.
How to tell apart: Streak differs, so Pararobertsite leaves brownish red, Mitridatite leaves olive-green; luster reads vitreous on Pararobertsite and dull, earthy to resinous on Mitridatite.
Often found alongside pararobertsite
Minerals reported to co-occur with pararobertsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Mn₃O₂(PO₄)₃(H₂O)₂·H₂O
- Mohs hardness
- 2
- Density
- 3.22 g/cm³
- Streak
- Brownish red
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Microcrystalline aggregates, crusts, powdery
- Cleavage
- Perfect on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in a complex zoned granite pegmatite
Where rockhounds find pararobertsite
Classic worldwide localities
- Tip Top mine, 8.5 km southwest of Custer, Custer Co., South Dakota, USA
Field-hunting tip
Where it forms: A rare secondary mineral in a complex zoned granite pegmatite. If you start seeing whitlockite, carbonate-apatite, quartz in float, you are in the right ground. Typical habit: microcrystalline aggregates, crusts, powdery. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pararobertsite?+
Where is pararobertsite found?+
What rocks look like pararobertsite?+
What minerals are found with pararobertsite?+
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Find pararobertsite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
