Frondelite is a rare phosphate mineral typically found as radial sprays of needle-like crystals or botryoidal masses in phosphate-rich pegmatites. Collectors prize its rich yellow to reddish-brown coloration and distinct fibrous habit. It is often identified as an alteration product of primary triphylite in complex pegmatite zones.
Is this frondelite?
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 frondelite with a known reference. Frondelite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Frondelite leaves a yellowish-brown streak.
- 3Read the lusterHold the specimen under a strong light. Frondelite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, brown, orange-brown, red-brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, radial, botryoidal, or acicular crystals.
Often confused with
Frondelite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Frondelite leaves yellowish-brown, Rockbridgeite leaves greenish-brown.
How to tell apart: Streak differs, so Frondelite leaves yellowish-brown, Dufrénite leaves light green.
How to tell apart: Streak differs, so Frondelite leaves yellowish-brown, Strengite leaves white.
Often found alongside frondelite
Minerals reported to co-occur with frondelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn²⁺Fe³⁺₄(PO₄)₃(OH)₅
- Mohs hardness
- 3.5-4
- Density
- 3.453 g/cm³
- Streak
- Yellowish-brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Radial, Botryoidal, Or Acicular Crystals
- Cleavage
- {100}, Excellent; {010}, Good; {001}, Fair
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
Where rockhounds find frondelite
Classic worldwide localities
- Minas Gerais, Brazil
- Hagendorf, Germany
- Mangualde, Portugal
- New Hampshire, USA
- South Dakota, USA
Field-hunting tip
Look in granite pegmatites country, the host setting where frondelite typically forms. If you start seeing triphylite, ludlamite, vivianite in float, you are in the right ground. Field specimens usually show a fibrous, radial, botryoidal, or acicular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find frondelite on the map
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