Fenaksite is a rare potassium-sodium-iron silicate found primarily in hyper-alkaline igneous complexes. Collectors usually seek it in its characteristic pink to reddish-brown tabular crystal form within pegmatite environments.
Is this fenaksite?
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 fenaksite with a known reference. Fenaksite sits at Mohs 5-5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly on cleavages.
- 4Match the color rangeCompare against the expected color range: brown, light pink.
- 5Look at form & habitCrystal system: triclinic. Typical habit: granular.
Often confused with
Fenaksite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads pearly on cleavages on Fenaksite and vitreous to greasy; fibrous aggregates are dull to silky on Serandite.
How to tell apart: Luster reads pearly on cleavages on Fenaksite and vitreous to dull on Eudialyte.
Often found alongside fenaksite
Minerals reported to co-occur with fenaksite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KNaFe²⁺Si₄O₁₀
- Mohs hardness
- 5-5.5
- Density
- 2.744 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly on cleavages
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Granular
- Cleavage
- Two intersecting at an angle of 122°
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In pegmatites associated with an ijolite-urtite intrusion in a differentiated alkalic massif
Where rockhounds find fenaksite
Classic worldwide localities
- Mts. Rasvumchorr and Yukspor, Khibiny massif, Kola Peninsula, Russia
Field-hunting tip
Where it forms: In pegmatites associated with an ijolite-urtite intrusion in a differentiated alkalic massif. If you start seeing albite, nepheline, aegirine-augite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find fenaksite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
