Grattarolaite is a rare iron phosphate that forms reddish brown microcrystalline nodules. It is very rare, occurring as microcrystalline nodules in lignite beds which appear to have burned naturally. It is associated with rodolicoite and heterosite. It was first described from the Castelnuovo mine, 30 km southeast of Florence, Florence, Italy.
Is this grattarolaite?
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 grattarolaite with a known reference. Grattarolaite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: greasy.
- 4Match the color rangeCompare against the expected color range: brown, red brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: aggregates.
Often confused with
Grattarolaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Grattarolaite leaves brown, Hematite leaves cherry-red or reddish brown; luster reads greasy on Grattarolaite and metallic or submetallic to dull on Hematite.
How to tell apart: Grattarolaite is noticeably harder (Mohs 6 vs. 4-4.5); streak differs, so Grattarolaite leaves brown, Bindheimite leaves white, yellowish white; luster reads greasy on Grattarolaite and resinous, dull, earthy on Bindheimite.
Often found alongside grattarolaite
Minerals reported to co-occur with grattarolaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe³⁺₃O₃(PO₄)
- Mohs hardness
- 6
- Density
- 4.07 g/cm³
- Streak
- Brown
- Luster
- Greasy
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Very rare, in microcrystalline nodules in lignite beds which appear to have burned naturally
Where rockhounds find grattarolaite
Classic worldwide localities
- Castelnuovo mine, Santa Barbara lignite district, 30 km southeast of Florence, Florence, Italy
Field-hunting tip
Where it forms: Very rare, in microcrystalline nodules in lignite beds which appear to have burned naturally. If you start seeing rodolicoite, heterosite in float, you are in the right ground. Typical habit: aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify grattarolaite?+
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What rocks look like grattarolaite?+
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Find grattarolaite on the map
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