Montroyalite is a rare strontium aluminum carbonate mineral known primarily from the Poudrette Quarry at Mont Saint-Hilaire. It typically forms as delicate, white, fibrous, or botryoidal clusters lining cavities in alkaline rocks. Due to its scarcity and association with other rare minerals, it is a highly sought-after species for mineralogists and serious collectors.
Is this montroyalite?
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 montroyalite with a known reference. Montroyalite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Montroyalite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Montroyalite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous aggregates, drusy coatings, botryoidal.
Often confused with
Montroyalite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside montroyalite
Minerals reported to co-occur with montroyalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Sr₄Al₈(CO₃)₃(OH,F)₂₆·10-11H₂O
- Mohs hardness
- 3.5
- Density
- 2.44 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous Aggregates, Drusy Coatings, Botryoidal
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Intrusions
- Typical price
- $50-300 per specimen
Where rockhounds find montroyalite
Classic worldwide localities
- Poudrette Quarry, Mont Saint-Hilaire, Quebec, Canada
Field-hunting tip
Look in alkaline igneous intrusions country — that is the host setting where montroyalite typically forms. If you start seeing dawsonite, strontianite, quartz in float, you are in the right ground. Field specimens usually show a fibrous aggregates, drusy coatings, botryoidal habit, so train your eye for that shape before scanning the outcrop.
Common questions
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How much is montroyalite worth?+
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Find montroyalite on the map
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