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. Grattarolaite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Grattarolaite typically shows a greasy luster.
- 4Match the color rangeCompare against the expected color range: reddish brown.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: in microcrystalline nodules.
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, Iron Ore leaves reddish-brown to black; luster reads greasy on Grattarolaite and metallic to submetallic on Iron Ore.
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 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
- 4.08 g/cm³
- Colors
- Streak
- Brown
- Luster
- Greasy
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- In Microcrystalline Nodules
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Manganese-rich Metamorphic Deposits
Where rockhounds find grattarolaite
Classic worldwide localities
- Cerchiara Mine, Liguria, Italy
Field-hunting tip
Look in manganese-rich metamorphic deposits country, the host setting where grattarolaite typically forms. If you start seeing hematite, quartz, braunite in float, you are in the right ground. Field specimens usually show a in microcrystalline nodules habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find grattarolaite on the map
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