Armstrongite is a rare calcium zirconium silicate typically found in hyper-alkaline pegmatites and igneous complexes. It usually forms as small, colorless to pale pink platy crystals or granular masses that require careful identification due to its similarity to other zirconium silicates.
Is this armstrongite?
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 armstrongite with a known reference. Armstrongite 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. Armstrongite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Armstrongite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, pale pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals, granular aggregates.
Often confused with
Armstrongite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside armstrongite
Minerals reported to co-occur with armstrongite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaZrSi₆O₁₅·3H₂O
- Mohs hardness
- 3.5
- Density
- 2.11 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals, Granular Aggregates
- Cleavage
- Good On {001}
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Alkaline Igneous Rocks, Pegmatites
- Typical price
- $20-100 per specimen depending on size and quality
Where rockhounds find armstrongite
Classic worldwide localities
- Khan-Bogdo massif, Gobi Desert, Mongolia
- Mont Saint-Hilaire, Quebec, Canada
- Gardar Province, Greenland
Field-hunting tip
Look in alkaline igneous rocks, pegmatites country — that is the host setting where armstrongite typically forms. If you start seeing quartz, microcline, aegirine in float, you are in the right ground. Field specimens usually show a platy crystals, granular aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find armstrongite on the map
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