Francoanellite is a rare phosphate mineral typically found as a secondary precipitate in cave guano deposits. It is often identified as soft, white, platy aggregates or crusts that form through the reaction of bat guano with aluminous bedrock or clay.
Is this francoanellite?
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 francoanellite with a known reference. Francoanellite 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. Francoanellite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Francoanellite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: trigonal. Typical habit: platy crystals, crusts, efflorescences.
Often confused with
Francoanellite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside francoanellite
Minerals reported to co-occur with francoanellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- H₆K₃Al₅(PO₄)₈·13H₂O
- Mohs hardness
- 2
- Density
- 1.96 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Platy Crystals, Crusts, Efflorescences
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Phosphate Deposits in Caves or Guano-rich Environments
- Typical price
- $50-300 per specimen
Where rockhounds find francoanellite
Classic worldwide localities
- Castellana Caves, Italy
- Petrohrad, Czech Republic
- Big Manistee River, USA
Field-hunting tip
Look in phosphate deposits in caves or guano-rich environments country — that is the host setting where francoanellite typically forms. If you start seeing taranakite, brushite, newberyite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts, efflorescences habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find francoanellite on the map
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