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 5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: deep bluish gray, gray-green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black, grayish green, bluish gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, radial, stellate.
Often confused with
Arfvedsonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Arfvedsonite leaves deep bluish gray, gray-green, Aegirine leaves pale yellowish gray.
How to tell apart: Streak differs, so Arfvedsonite leaves deep bluish gray, gray-green, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Arfvedsonite leaves deep bluish gray, gray-green, Riebeckite leaves greenish brown.
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
- 5-6
- Density
- 3.44-3.45 g/cm³
- Streak
- Deep bluish gray, gray-green
- Luster
- Vitreous
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, radial, stellate
- Cleavage
- Perfect on {110}, with intersections of 56° and 124°; parting on {010}
- Rarity
- Uncommon
- Uses
- Collector, Lapidary
- Host rock
- Common in alkalic granites and other alkalic plutonic rocks and pegmatites
Where rockhounds find arfvedsonite
Classic worldwide localities
- St. Peters Dome, near Pikes Peak, El Paso Co., Colorado, USA
- Hurricane Mountain, Intervale, Carroll Co., New Hampshire, USA
- Magnet Cove, Hot Spring Co., Arkansas, USA
- Burnsville, Yancey Co., North Carolina, USA
- Langesundsfjord, Norway
- Buchans, Newfoundland, and Mont Saint-Hilaire, Quebec, Canada
Field-hunting tip
Where it forms: Common in alkalic granites and other alkalic plutonic rocks and pegmatites. If you start seeing nepheline, albite, aegirine in float, you are in the right ground. Typical habit: fibrous, radial, stellate. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify arfvedsonite?+
Where is arfvedsonite found?+
What rocks look like arfvedsonite?+
What minerals are found with arfvedsonite?+
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What is arfvedsonite used for?+
Find arfvedsonite on the map
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