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 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Giniite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Giniite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark green, brownish green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals.
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 3.5 vs. 1.5-2); streak differs — Giniite leaves white, Vivianite leaves white to light blue.
How to tell apart: Rockbridgeite is the harder of the two (Mohs 4.5 vs. 3.5); streak differs — Giniite leaves white, Rockbridgeite leaves greenish-brown.
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
- Fe²⁺Fe³⁺₄(PO₄)₃(OH)₅·2H₂O
- Mohs hardness
- 3.5
- Density
- 3.1 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $50-300 per specimen
Where rockhounds find giniite
Classic worldwide localities
- Tip Top Mine, South Dakota, USA
- Hagendorf-Pleystein, Bavaria, Germany
Field-hunting tip
Look in granite pegmatites country — that is the host setting where giniite typically forms. If you start seeing triphylite, rockbridgeite, frondelite in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find giniite on the map
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