Wilkinsonite is a very rare member of the aenigmatite group typically found as dark, opaque crystals in alkaline igneous environments. It is most notable for being found in high-alkaline pegmatite complexes like those at Mont Saint-Hilaire, often appearing as dark, lustrous prismatic clusters.
Is this wilkinsonite?
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 wilkinsonite with a known reference. Wilkinsonite 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: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic crystals, anhedral grains.
Often confused with
Wilkinsonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Wilkinsonite leaves brown, Aenigmatite leaves reddish brown.
How to tell apart: Streak differs, so Wilkinsonite leaves brown, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Wilkinsonite leaves brown, Arfvedsonite leaves deep bluish gray, gray-green.
Often found alongside wilkinsonite
Minerals reported to co-occur with wilkinsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Fe²⁺₄Fe³⁺₂Si₆O₂₀
- Mohs hardness
- ~5
- Density
- 3.89 g/cm³
- Colors
- Streak
- Brown
- Luster
- Vitreous
- Transparency
- Opaque to semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Prismatic crystals, anhedral grains
- Cleavage
- Distinct on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In an eruptive peralkaline trachyte (Warrumbungle volcano, Australia); in syenite ejecta (Wonchi volcano, Ethiopia)
Where rockhounds find wilkinsonite
Classic worldwide localities
- Warrumbungle volcano and associated Bingie Grumble Mountain, New South Wales, Australia
- Wonchi volcano, 90 km south of Addis Ababa, Ethiopia
Field-hunting tip
Where it forms: In an eruptive peralkaline trachyte (Warrumbungle volcano, Australia); in syenite ejecta (Wonchi volcano, Ethiopia). If you start seeing anorthoclase, sodalite, clinopyroxenes in float, you are in the right ground. Typical habit: prismatic crystals, anhedral grains. Train your eye for that shape before scanning the outcrop.
Common questions
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Find wilkinsonite on the map
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