Thornasite is an extremely rare zirconium silicate mineral primarily found in the alkaline intrusive complex of Mont Saint-Hilaire in Quebec, Canada. It typically presents as small tabular crystals or massive aggregates within pegmatite vugs, often appearing alongside other exotic rare-earth minerals. Collectors prize it for its unique chemistry and extreme rarity within the alkaline rock petrogenesis group.
Is this thornasite?
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 thornasite with a known reference. Thornasite sits at Mohs 5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Thornasite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Thornasite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, pinkish.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals, massive, granular.
Often confused with
Thornasite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside thornasite
Minerals reported to co-occur with thornasite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₁₂Zr₃Si₂₂O₅₇·18H₂O
- Mohs hardness
- 5
- Density
- 2.36 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Tabular Crystals, Massive, Granular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Agpaitic Syenite Pegmatites
- Typical price
- $50-300 per specimen
Where rockhounds find thornasite
Classic worldwide localities
- Mont Saint-Hilaire, Canada
Field-hunting tip
Look in agpaitic syenite pegmatites country — that is the host setting where thornasite typically forms. If you start seeing aegirine, microcline, sodalite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find thornasite on the map
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