Rasvumite is a rare potassium iron sulfide typically found as dark, metallic, needle-like or prismatic crystals in alkaline pegmatites. It is best known from the Khibiny Massif in Russia, where it occurs within hyper-agpaitic rocks associated with minerals like aegirine and nepheline.
Is this rasvumite?
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 rasvumite with a known reference. Rasvumite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Rasvumite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Rasvumite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black, dark brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, acicular, radiating aggregates.
Often confused with
Rasvumite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 3); streak differs — Rasvumite leaves black, Pyrite leaves greenish-black to brownish-black.
How to tell apart: Streak differs — Rasvumite leaves black, Chalcopyrite leaves greenish-black.
Often found alongside rasvumite
Minerals reported to co-occur with rasvumite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe₂S₃
- Mohs hardness
- 3
- Density
- 3.37 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Acicular, Radiating Aggregates
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Pegmatites
- Typical price
- $50-300 per specimen depending on size and association
Where rockhounds find rasvumite
Classic worldwide localities
- Rasvumchorr Mountain, Khibiny Massif, Russia
- Kola Peninsula, Russia
Field-hunting tip
Look in alkaline igneous pegmatites country — that is the host setting where rasvumite typically forms. If you start seeing aegirine, nepheline, kalsilite in float, you are in the right ground. Field specimens usually show a prismatic crystals, acicular, radiating aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find rasvumite on the map
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