Magnesioneptunite is a rare silicate mineral belonging to the neptunite group, distinguished by the dominance of magnesium in its structure. It typically occurs as dark, prismatic crystals embedded in white natrolite matrices, most famously alongside benitoite at the Dallas Gem Mine in California.
Is this magnesioneptunite?
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 magnesioneptunite with a known reference. Magnesioneptunite 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. Magnesioneptunite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Magnesioneptunite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark red, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals.
Often confused with
Magnesioneptunite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside magnesioneptunite
Minerals reported to co-occur with magnesioneptunite. 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
- 3.23 g/cm³
- Streak
- Brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals
- Cleavage
- Distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Glaucophane Schist
- Typical price
- $50-500 depending on specimen size and association with benitoite
Where rockhounds find magnesioneptunite
Classic worldwide localities
- San Benito County, California, USA
- Kola Peninsula, Russia
Field-hunting tip
Look in glaucophane schist country — that is the host setting where magnesioneptunite 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 magnesioneptunite?+
Where is magnesioneptunite found?+
How much is magnesioneptunite worth?+
What rocks look like magnesioneptunite?+
What minerals are found with magnesioneptunite?+
What kind of rock does magnesioneptunite form in?+
What is magnesioneptunite used for?+
Find magnesioneptunite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
