Mountainite is a rare phyllosilicate mineral that typically forms soft, white, platy, or micaceous aggregates within hydrothermal vugs. Collectors should look for its distinctive pearly luster and association with other zeolites and related silicate minerals in alkaline environments.
Is this mountainite?
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 mountainite with a known reference. Mountainite sits at Mohs 3, 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: silky.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: felted, lath, rosette.
Often confused with
Mountainite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Apophyllite is the harder of the two (Mohs 4-5 vs. 3); luster reads silky on Mountainite and vitreous to pearly on Apophyllite.
How to tell apart: Pectolite is the harder of the two (Mohs 4.5-5 vs. 3).
How to tell apart: Okenite is the harder of the two (Mohs 5 vs. 3); luster reads silky on Mountainite and vitreous to pearly on Okenite.
Often found alongside mountainite
Minerals reported to co-occur with mountainite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KNa₂Ca₂Si₈O₁₉(OH)·6H₂O
- Mohs hardness
- 3
- Density
- 2.36 g/cm³
- Colors
- Streak
- White
- Luster
- Silky
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Felted, lath, rosette
- Cleavage
- {001} (?)
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a kimberlite pipe (Kimberley, South Africa); in a differentiated alkalic massif (Lovozero massif, Russia)
Where rockhounds find mountainite
Classic worldwide localities
- Bultfontein diamond mine, Kimberley, Cape Province, South Africa
- Mt. Karnasurt, Lovozero massif, Kola Peninsula, Russia
- Höwenegg quarry, Hegau, Baden-Württemberg, Germany
Field-hunting tip
Where it forms: In a kimberlite pipe (Kimberley, South Africa); in a differentiated alkalic massif (Lovozero massif, Russia). If you start seeing rhodesite, natrolite, steenstrupine in float, you are in the right ground. Typical habit: felted, lath, rosette. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mountainite?+
Where is mountainite found?+
What rocks look like mountainite?+
What minerals are found with mountainite?+
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Find mountainite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
