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?
4-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.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 3Match the color rangeCompare against the expected color range: dark brown, red-brown.
- 4Look 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
- KNa₂LiMg₂Ti₂Si₈O₂₄
- Mohs hardness
- 5-6
- Density
- 3.152 g/cm³
- Colors
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals
- Cleavage
- Perfect on {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In volcanic ejecta of hornfelsed fine-grained sandstone as reaction zones between a skarn carbonate xenolith and host ignimbrite by alteration of ilmenite
Where rockhounds find magnesioneptunite
Classic worldwide localities
- Upper Chegem (Verkhnechegemskaya) Caldera near Mount Lakargi in the interfluve of the Chegem and Kenstanta Rivers, Kabardino-Balkaria, Northern Caucasus, Russia
Field-hunting tip
Where it forms: In volcanic ejecta of hornfelsed fine-grained sandstone as reaction zones between a skarn carbonate xenolith and host ignimbrite by alteration of ilmenite. If you start seeing quartz, sanidine, microcline in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesioneptunite?+
Where is magnesioneptunite found?+
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.
