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. Mountainite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mountainite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy or micaceous aggregates.
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 4.5-5 vs. 3); luster reads pearly 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); luster reads pearly on Mountainite and vitreous to silky on Pectolite.
How to tell apart: Okenite is the harder of the two (Mohs 4.5-5 vs. 3).
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
- 2.28 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy or Micaceous Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Complexes and Hydrothermal Cavities in Basalt
- Typical price
- $50-300 per specimen depending on size and quality
Where rockhounds find mountainite
Classic worldwide localities
- Bultfontein mine, South Africa
- Wessels mine, South Africa
- Khibiny massif, Russia
Field-hunting tip
Look in alkaline igneous complexes and hydrothermal cavities in basalt country — that is the host setting where mountainite typically forms. If you start seeing calcite, apophyllite, natrolite in float, you are in the right ground. Field specimens usually show a platy or micaceous aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find mountainite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
