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, so 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, so 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, 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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