Johnwalkite is a rare phosphate mineral typically found in complex granite pegmatites. It usually forms small, yellowish-brown tabular crystals and is highly sought after by systematic mineral collectors due to its scarcity.
Is this johnwalkite?
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 johnwalkite with a known reference. Johnwalkite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: medium greenish yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark reddish brown, reddish brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates, prismatic, radial.
Often confused with
Johnwalkite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Johnwalkite leaves medium greenish yellow, Wolfeite leaves white.
How to tell apart: Triplite is the harder of the two (Mohs 5-5.5 vs. 4); streak differs, so Johnwalkite leaves medium greenish yellow, Triplite leaves white to brown.
Often found alongside johnwalkite
Minerals reported to co-occur with johnwalkite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KMn₂NbO₂(PO₄)₂(H₂O)₂
- Mohs hardness
- 4
- Density
- 3.40 g/cm³
- Streak
- Medium greenish yellow
- Luster
- Vitreous
- Transparency
- Opaque, transparent on thin edges
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates, prismatic, radial
- Cleavage
- Good on {001} and {100}; poor on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral derived from the dissolution of triphylite-lithiophilite and columbite-tantalite in a complex granite pegmatite
Where rockhounds find johnwalkite
Classic worldwide localities
- Expectation pegmatite at the Champion mine, about 2.5 km southeast of Keystone, Pennington Co., South Dakota, USA
Field-hunting tip
Where it forms: A rare secondary mineral derived from the dissolution of triphylite-lithiophilite and columbite-tantalite in a complex granite pegmatite. If you start seeing fluorapatite, childrenite-eosphorite, rockbridgeite-frondelite in float, you are in the right ground. Typical habit: aggregates, prismatic, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify johnwalkite?+
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What rocks look like johnwalkite?+
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Find johnwalkite on the map
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