Rustenburgite is an extremely rare platinum-tin intermetallic mineral typically found as microscopic inclusions within other platinum group minerals. It is primarily identified through advanced laboratory analysis like scanning electron microscopy in layered igneous intrusions. Specimens are generally limited to small grains or inclusions rather than large distinct crystals.
Is this rustenburgite?
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 rustenburgite with a known reference. Rustenburgite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: tin white.
- 5Look at form & habitCrystal system: cubic. Typical habit: granular.
Often confused with
Rustenburgite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Sperrylite is the harder of the two (Mohs 6-7 vs. 5); streak differs, so Rustenburgite leaves gray, Sperrylite leaves black.
How to tell apart: Streak differs, so Rustenburgite leaves gray, Cooperite leaves black.
How to tell apart: Streak differs, so Rustenburgite leaves gray, Platinum leaves grayish white.
Often found alongside rustenburgite
Minerals reported to co-occur with rustenburgite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pt₃Sn
- Mohs hardness
- 5
- Density
- 15.08 g/cm³
- Colors
- Streak
- Gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Granular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As very sparse grains in concentrates (Merensky Reef, South Africa)
Where rockhounds find rustenburgite
Classic worldwide localities
- Upper Banded Zone of the Stillwater complex, Montana, USA
- Rustenburg (type locality), Atok, and Onverwacht mines, on the Merensky Reef, Bushveld complex, Transvaal, South Africa
- Noril’sk, western Siberia, Russia
- Ioko-Dovyren ultramafic pluton, northern Baikal district, eastern Siberia, Russia
Field-hunting tip
Where it forms: As very sparse grains in concentrates (Merensky Reef, South Africa). If you start seeing atokite, unspecified platinum tellurides, moncheite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find rustenburgite on the map
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