Neptunite is prized by collectors for its striking, square-prismatic black crystals that often occur in sharp, contrast-rich association with white natrolite and blue benitoite. It is most famous for specimens from the California Gem Mine where it forms distinct, elongated crystals. While chemically complex, its combination of high-luster black crystals and specific geological associations makes it a highly sought-after mineral specimen.
Is this neptunite?
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 neptunite with a known reference. Neptunite 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. Neptunite leaves a brownish red streak.
- 3Read the lusterHold the specimen under a strong light. Neptunite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, deep red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals.
Often confused with
Neptunite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside neptunite
Minerals reported to co-occur with neptunite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KNa₂Li(Fe²⁺,Mg,Mn)₂Ti₂Si₈O₂₄
- Mohs hardness
- 5-6
- Density
- 3.19-3.23 g/cm³
- Streak
- Brownish Red
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals
- Cleavage
- Distinct On {110}
- Rarity
- Rare
- Uses
- Collector, Specimen
- Host rock
- Glaucophane Schist and Hydrothermal Veins
- Typical price
- $50-500 thumbnail, $300-2000+ cabinet
Where rockhounds find neptunite
Classic worldwide localities
- San Benito County, California, USA
- Khibiny Massif, Russia
- Mont Saint-Hilaire, Canada
Field-hunting tip
Look in glaucophane schist and hydrothermal veins country — that is the host setting where neptunite typically forms. If you start seeing benitoite, natrolite, joaquinite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify neptunite?+
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How much is neptunite worth?+
What rocks look like neptunite?+
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Find neptunite on the map
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