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, 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
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
