Ardealite is a rare phosphate-sulfate mineral that typically forms through the reaction of bat guano with limestone bedrock in cave environments. It is most commonly found as earthy, white to yellowish massive coatings or crusts and is often visually indistinguishable from related phosphate minerals without laboratory analysis.
Is this ardealite?
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 ardealite with a known reference. Ardealite sits at Mohs 1-1.5, 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: earthy.
- 4Match the color rangeCompare against the expected color range: light yellow, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: encrustations, powdery.
Often confused with
Ardealite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads earthy on Ardealite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Brushite is the harder of the two (Mohs 2.5 vs. 1-1.5); luster reads earthy on Ardealite and vitreous, pearly on cleavages on Brushite.
Often found alongside ardealite
Minerals reported to co-occur with ardealite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂(SO₄)(HPO₄)·4H₂O
- Mohs hardness
- 1-1.5
- Density
- 2.34 g/cm³
- Colors
- Streak
- White
- Luster
- Earthy
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Encrustations, powdery
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In limestone caves, as an early stage of the breakdown of bat guano, in reaction with calcite
Where rockhounds find ardealite
Classic worldwide localities
- Cioclovina Cave, Transylvania, Romania
- La Guangola Cave, near Altamura, Apulia, Italy
- Magurata and Bacho Kuo Caves, Bulgaria
- Baobab and Uisib Caves, Namibia
- Moora Pave Cave, Jurien Bay, Western Australia
- Onino-Iwaya Cave, Hiroshima Prefecture, Japan
Field-hunting tip
Where it forms: In limestone caves, as an early stage of the breakdown of bat guano, in reaction with calcite. If you start seeing brushite, gypsum, carbonate-hydroxylapatite in float, you are in the right ground. Typical habit: encrustations, powdery. Train your eye for that shape before scanning the outcrop.
Common questions
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Find ardealite on the map
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