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, 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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Find montroyalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
