Putnisite is a remarkably rare and chemically unique mineral discovered in Western Australia. It typically appears as small, vibrant pink to violet pseudocubic crystals on a white matrix, often found in association with other strontium-bearing minerals.
Is this putnisite?
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 putnisite with a known reference. Putnisite sits at Mohs 1.5-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pink.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: pale, dark purple.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: pseudocubic crystals.
Often confused with
Putnisite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Strontianite is the harder of the two (Mohs 3.5 vs. 1.5-2); streak differs, so Putnisite leaves pink, Strontianite leaves white.
How to tell apart: Ankerite is the harder of the two (Mohs 3.5-4 vs. 1.5-2); streak differs, so Putnisite leaves pink, Ankerite leaves white.
Often found alongside putnisite
Minerals reported to co-occur with putnisite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SrCa₄Cr⁸⁺₈(CO₃)₈SO₄(OH)₁₆·25H₂O
- Mohs hardness
- 1.5-2
- Density
- 2.20 g/cm³
- Colors
- PaleDark purple
- Streak
- Pink
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Pseudocubic crystals
- Cleavage
- One excellent and two good parallel to {100}, {010}, and {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A product of the oxidation of a massive nickel sulfide deposit in komatiitic/dioritic rocks
Where rockhounds find putnisite
Classic worldwide localities
- Halls Knoll gossan, Polar Bear peninsula, Southern Lake Cowan, 40 km north of Norseman, Western Australia, Australia
Field-hunting tip
Where it forms: A product of the oxidation of a massive nickel sulfide deposit in komatiitic/dioritic rocks. If you start seeing quartz in float, you are in the right ground. Typical habit: pseudocubic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify putnisite?+
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What rocks look like putnisite?+
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Find putnisite on the map
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