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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous.
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)₂₆·10H₂O
- Mohs hardness
- 3.5
- Density
- 2.677 g/cm³
- Colors
- Streak
- White
- Luster
- Dull
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In cavities in a silicocarbonate sill
Where rockhounds find montroyalite
Classic worldwide localities
- Francon quarry, Montreal Island, Montreal, Quebec, Canada
Field-hunting tip
Where it forms: In cavities in a silicocarbonate sill. If you start seeing albite, strontiodresserite, calcite in float, you are in the right ground. Typical habit: fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify montroyalite?+
Where is montroyalite found?+
What rocks look like montroyalite?+
What minerals are found with montroyalite?+
What kind of rock does montroyalite form in?+
What is montroyalite used for?+
Find montroyalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
