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Neptunite
Neptunite is silicates (titanosilicate), KNa2Li(Fe,Mn)2Ti2Si8O24. In the hand, it rates 5 to 6 on the Mohs scale, and it runs black with deep red glints. Jet-black prisms with square-ish cross sections and blood-red internal flashes on edges, classically embedded in snow-white natrolite with blue benitoite.
The geology.
Neptunite carries the formula KNa2Li(Fe,Mn)2Ti2Si8O24. It belongs to the monoclinic system. Catalogues list it as silicates (titanosilicate).
It sits at 5 to 6 on the Mohs scale. The surface reads vitreous. Light behaviour is opaque; deep red internal reflections on thin edges. Specific gravity runs 3.19 to 3.23. The streak is red-brown. It breaks with perfect cleavage; conchoidal fracture.
Jet-black prisms with square-ish cross sections and blood-red internal flashes on edges, classically embedded in snow-white natrolite with blue benitoite.
It reaches buyers as prismatic crystals with square cross-section, crystals in white natrolite or matrix specimens.
The origins.
Benitoite Gem mine, San Benito County, California (world classic); Greenland and Russia (alkaline complexes).
On value, the database notes: collector mineral; California matrix pieces with benitoite are premium.
Traditional associations.
In energy work traditions, associated with depth psychology and exploring the unconscious.
We keep this section because people ask. It sits below the geology on purpose, and none of it describes something the stone does.
Spotting the real thing.
Jet-black prisms with square-ish cross sections and blood-red internal flashes on edges, classically embedded in snow-white natrolite with blue benitoite.
Not faked; repaired crystals reset in natrolite paste exist, inspect contacts.
| Looks like | How to tell them apart |
|---|---|
| Black tourmaline | Tourmaline cross-sections are rounded triangles and streak white; neptunite streaks red-brown |
| Aegirine | Aegirine blades are steeply pointed and streak pale gray-green |
| Augite | Augite is duller, streaks greenish gray, and lacks red edge glints |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on neptunite.
| Test | What you should see |
|---|---|
| By eye | Red-brown streak from a black crystal |
| By eye | Deep red translucence on thin edges with strong light |
| By eye | Association with natrolite and benitoite (California) |
Stop short of anything that leaves a mark. A gemologist can answer the rest without damaging the stone.
Care & handling.
At 5 to 6 on the Mohs scale it handles careful wear but scratches against quartz and dust. Store it separately and take rings off before rough work.
It breaks with perfect cleavage; conchoidal fracture, which is worth knowing before you set it or drop it.
Skip the ultrasonic. Lukewarm water, mild soap and a soft cloth handle routine cleaning without risk.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is KNa2Li(Fe,Mn)2Ti2Si8O24. Crystal system: Monoclinic. Specific gravity: 3.19 to 3.23. Streak: Red-brown. Cleavage and fracture: Perfect cleavage; conchoidal fracture.
How it reaches the market
Benitoite Gem mine, San Benito County, California (world classic); Greenland and Russia (alkaline complexes).
What it gets confused with
Black tourmaline: Tourmaline cross-sections are rounded triangles and streak white; neptunite streaks red-brown. Aegirine: Aegirine blades are steeply pointed and streak pale gray-green. Augite: Augite is duller, streaks greenish gray, and lacks red edge glints.
What it is worth
Collector mineral; California matrix pieces with benitoite are premium.
Where buyers get caught
Not faked; repaired crystals reset in natrolite paste exist, inspect contacts.
One more thing
Neptunite shares its only famous pocket with benitoite, California's state gem, dealers etch the white natrolite with acid to reveal hidden black prisms.
An education-first guide.
We do not carry neptunite. This page exists because the question comes up and the honest answer is worth writing down, whether or not there is anything here to sell you.
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