Arfvedsonite is a dark, sodium-rich amphibole typically found as elongated, blade-like, or radiating crystals in alkaline rocks. It is highly prized by collectors for its sharp, lustrous, dark prisms that often appear jet black, though they may show deep bluish hues under strong light.
Is this 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 arfvedsonite with a known reference. Arfvedsonite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Arfvedsonite leaves a grey to bluish-grey streak.
- 3Read the lusterHold the specimen under a strong light. Arfvedsonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark blue-black, dark green-black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic to acicular, often radiating or bladed aggregates.
Often confused with
Arfvedsonite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Arfvedsonite leaves grey to bluish-grey, Aegirine leaves yellowish-grey.
How to tell apart: Streak differs — Arfvedsonite leaves grey to bluish-grey, Hornblende leaves grayish-white.
How to tell apart: Streak differs — Arfvedsonite leaves grey to bluish-grey, Riebeckite leaves blue-gray.
Often found alongside arfvedsonite
Minerals reported to co-occur with arfvedsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- [Na][Na₂][Fe²⁺₄Fe³⁺][Si₈O₂₂](OH)₂
- Mohs hardness
- 5.5-6
- Density
- 3.33-3.48 g/cm³
- Streak
- Grey to Bluish-grey
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic to Acicular, Often Radiating or Bladed Aggregates
- Cleavage
- Perfect in Two Directions At 56 and 124 Degrees
- Rarity
- Uncommon
- Uses
- Collector, Lapidary
- Host rock
- Alkaline Igneous Rocks, Syenites, And Nepheline Syenites
- Typical price
- $10-100 depending on specimen size and clarity of bladed habit
Where rockhounds find arfvedsonite
Classic worldwide localities
- Kangerlussuaq, Greenland
- Mont Saint-Hilaire, Quebec, Canada
- Kola Peninsula, Russia
- Narssarssuk, Greenland
Field-hunting tip
Look in alkaline igneous rocks, syenites, and nepheline syenites country — that is the host setting where arfvedsonite typically forms. If you start seeing nepheline, aegirine, microcline in float, you are in the right ground. Field specimens usually show a prismatic to acicular, often radiating or bladed aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify arfvedsonite?+
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What rocks look like arfvedsonite?+
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Find arfvedsonite on the map
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