Taranakite is a rare phosphate mineral formed by the reaction of guano-derived phosphoric acid with aluminous rocks, typically found in limestone caves. It usually occurs as fine-grained, chalky-looking masses or thin crusts that exhibit a characteristic pearly luster upon close inspection.
Is this taranakite?
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 taranakite with a known reference. Taranakite sits at Mohs 1-2, 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: pearly.
- 4Match the color rangeCompare against the expected color range: white, gray white, yellowish white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: fine-grained aggregates, crusts, rosettes.
Often confused with
Taranakite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Variscite is the harder of the two (Mohs 4.5 vs. 1-2); luster reads pearly on Taranakite and vitreous to waxy on Variscite.
How to tell apart: Wavellite is the harder of the two (Mohs 3.5-4 vs. 1-2); luster reads pearly on Taranakite and vitreous to resinous, pearly on Wavellite.
Often found alongside taranakite
Minerals reported to co-occur with taranakite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₃Al₅(PO₄)₂(HPO₄)₆·18H₂O
- Mohs hardness
- 1-2
- Density
- 2.12-2.15 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Fine-grained aggregates, crusts, rosettes
- Cleavage
- Perfect basal
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Formed from phosphatic solutions derived from bird or bat guano reacting with clays or aluminous rocks under perenially damp conditions; the most common phosphate mineral in caves
Where rockhounds find taranakite
Classic worldwide localities
- Pig Hole Cave, Giles Co., Virginia, USA
- Low Water Bridge Cave, Greene Co., Missouri, USA
- Sugarloaves, near New Plymouth, Taranaki Peninsula, New Zealand
- Réunion Island, Indian Ocean
- Island Leones, Patagonia, Argentina
- King George Island, Maritime Antarctic
Field-hunting tip
Where it forms: Formed from phosphatic solutions derived from bird or bat guano reacting with clays or aluminous rocks under perenially damp conditions; the most common phosphate mineral in caves. If you start seeing vashegyite, leucophosphite, minyulite in float, you are in the right ground. Typical habit: fine-grained aggregates, crusts, rosettes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify taranakite?+
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What rocks look like taranakite?+
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Find taranakite on the map
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