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 — Frondelite leaves yellowish-brown, Rockbridgeite leaves greenish-brown.
How to tell apart: Streak differs — Frondelite leaves yellowish-brown, Dufrénite leaves light green.
How to tell apart: Streak differs — 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
- 3.8-3.9 g/cm³
- Streak
- Yellowish-brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Radial, Botryoidal, Or Acicular Crystals
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $20-200 thumbnail, $150-800 cabinet
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 — that is 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
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
