Tvrdýite is a rare aluminum phosphate mineral related to variscite, typically found as attractive botryoidal crusts or nodules within phosphate-rich sedimentary sequences. Collectors value it for its vibrant green hues and distinctive waxy luster when found in high-quality cabinet specimens.
Is this tvrdýite?
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 tvrdýite with a known reference. Tvrdýite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light olive-green.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: silvery, olive grayish green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: botryoidal, crusts, massive.
Often confused with
Tvrdýite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Tvrdýite leaves light olive-green, Variscite leaves white; luster reads pearly on Tvrdýite and vitreous to waxy on Variscite.
How to tell apart: Wardite is the harder of the two (Mohs 5 vs. 3-4); streak differs, so Tvrdýite leaves light olive-green, Wardite leaves white; luster reads pearly on Tvrdýite and vitreous on Wardite.
Often found alongside tvrdýite
Minerals reported to co-occur with tvrdýite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeFe₂Al₃(PO₄)₄(OH)₅(H₂O)₄·2H₂O
- Mohs hardness
- 3-4
- Density
- 2.834 g/cm³
- Colors
- SilveryOlive grayish green
- Streak
- Light olive-green
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Botryoidal, crusts, massive
- Cleavage
- Good on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a cavity in quartz in greisened granite, probably a late hydrothermal or supergene mineral formed from the breakdown of primary triplite (in association with isokite and fluorapatite) in contact with acidic waters
Where rockhounds find tvrdýite
Classic worldwide localities
- Huber open pit, Krásno ore district, near Horní Slavkov, western Bohemia, Czech Republic
Field-hunting tip
Where it forms: In a cavity in quartz in greisened granite, probably a late hydrothermal or supergene mineral formed from the breakdown of primary triplite (in association with isokite and fluorapatite) in contact with acidic waters. If you start seeing al-rich beraunite, fluorapatite, pharmacosiderite in float, you are in the right ground. Typical habit: botryoidal, crusts, massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find tvrdýite on the map
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