Polydymite is a rare nickel sulfide mineral often found within complex nickel-copper ore bodies. It typically presents as metallic, grayish-white masses or small octahedra, frequently occurring as a replacement for other nickel-bearing sulfides like pentlandite.
Is this polydymite?
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 polydymite with a known reference. Polydymite sits at Mohs 4.5-5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic, brilliant on fresh surface.
- 4Match the color rangeCompare against the expected color range: violet gray, copper red, light gray, steel gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: massive, octahedral crystals, twinning common.
Often confused with
Polydymite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Polydymite leaves black gray, Linnaeite leaves grayish black.
How to tell apart: Streak differs, so Polydymite leaves black gray, Pentlandite leaves pale bronze-brown.
Often found alongside polydymite
Minerals reported to co-occur with polydymite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NiNi₂S₄
- Mohs hardness
- 4.5-5.5
- Density
- 4.5-4.8 g/cm³
- Colors
- Streak
- Black gray
- Luster
- Metallic, brilliant on fresh surface
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive, octahedral crystals, twinning common
- Cleavage
- Imperfect on {001}; reported on {111}
- Rarity
- Rare
- Uses
- Collector, Ore of nickel
- Host rock
- In hydrothermal veins
Where rockhounds find polydymite
Classic worldwide localities
- Hamilton, Hancock Co., Illinois, USA
- Miliken (Sweetwater) mine, Reynolds Co., Missouri, USA
- Copper King mine, Gold Hill district, Boulder Co., Colorado, USA
- Grünau mine, Daaden, near Siegen (type locality), and at Ramsbeck, North Rhine-Westphalia, Germany
- Saint Marina, Khaskovo district, Bulgaria
- Kunratice and Rozany, Czech Republic
Field-hunting tip
Where it forms: In hydrothermal veins. If you start seeing chalcopyrite, pyrrhotite, pyrite in float, you are in the right ground. Typical habit: massive, octahedral crystals, twinning common. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify polydymite?+
Where is polydymite found?+
Is polydymite safe to handle?+
What rocks look like polydymite?+
What minerals are found with polydymite?+
What kind of rock does polydymite form in?+
What is polydymite used for?+
Find polydymite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
