Potassic-arfvedsonite is a rare member of the amphibole group found primarily in alkaline igneous environments. Collectors identify it by its dark, elongated prismatic crystals which often appear as part of complex mineral assemblages in syenites and nepheline syenites.
Is this potassic-arfvedsonite?
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 potassic-arfvedsonite with a known reference. Potassic-arfvedsonite sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Potassic-arfvedsonite leaves a grey to green streak.
- 3Read the lusterHold the specimen under a strong light. Potassic-arfvedsonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark green, black, blue-black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic to acicular crystals, often elongated or fibrous.
Often confused with
Potassic-arfvedsonite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Potassic-arfvedsonite leaves grey to green, Arfvedsonite leaves grey to bluish-grey.
How to tell apart: Streak differs — Potassic-arfvedsonite leaves grey to green, Riebeckite leaves blue-gray.
How to tell apart: Streak differs — Potassic-arfvedsonite leaves grey to green, Hastingsite leaves white to light gray.
Often found alongside potassic-arfvedsonite
Minerals reported to co-occur with potassic-arfvedsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KNa₂Fe²⁺₄Fe³⁺Si₈O₂₂F₂
- Mohs hardness
- 5-6
- Density
- 3.3-3.5 g/cm³
- Streak
- Grey to Green
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic to Acicular Crystals, Often Elongated or Fibrous
- Cleavage
- Perfect On {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Rocks
- Typical price
- $20-150 per specimen
Where rockhounds find potassic-arfvedsonite
Classic worldwide localities
- Canada
- Greenland
- Russia
- Norway
Field-hunting tip
Look in alkaline igneous rocks country — that is the host setting where potassic-arfvedsonite typically forms. If you start seeing nepheline, albite, aegirine in float, you are in the right ground. Field specimens usually show a prismatic to acicular crystals, often elongated or fibrous habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find potassic-arfvedsonite on the map
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