Giniite is an exceptionally rare iron phosphate mineral that typically occurs as small, dark green, platy crystals. It is primarily found as an alteration product within phosphate-rich zones of granitic pegmatites, often closely associated with other iron phosphates like rockbridgeite and frondelite.
Is this giniite?
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 giniite with a known reference. Giniite 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: olive-green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to greasy.
- 4Match the color rangeCompare against the expected color range: blackish brown, black, blackish green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crystalline.
Often confused with
Giniite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Giniite is noticeably harder (Mohs 3-4 vs. 1.5-2); streak differs, so Giniite leaves olive-green, Vivianite leaves white, altering to dark blue, brown.
How to tell apart: Streak differs, so Giniite leaves olive-green, Rockbridgeite leaves greenish gray.
Often found alongside giniite
Minerals reported to co-occur with giniite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeFe₄(PO₄)₄(OH)₂·2H₂O
- Mohs hardness
- 3-4
- Density
- 3.41 g/cm³
- Streak
- Olive-green
- Luster
- Vitreous to greasy
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Crystalline
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in a complex granite pegmatite
Where rockhounds find giniite
Classic worldwide localities
- Sandamap pegmatite, west of Usakos, Namibia
Field-hunting tip
Where it forms: A secondary mineral in a complex granite pegmatite. If you start seeing triphylite, barbosalite, huréaulite in float, you are in the right ground. Typical habit: crystalline. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify giniite?+
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What rocks look like giniite?+
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Find giniite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
