Thomsonite is a member of the zeolite group most commonly found in amygdaloidal basalt, occurring as radiating fibrous aggregates that form colorful, banded nodules. Collectors highly prize these for their concentric patterns and chatoyancy when cut and polished by lapidaries.
Is this thomsonite nodules?
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 thomsonite nodules with a known reference. Thomsonite Nodules sits at Mohs 5-5.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Thomsonite Nodules leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Thomsonite Nodules typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, pink, green, tan, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: radial fibrous nodules.
Often confused with
Thomsonite Nodules vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside thomsonite nodules
Minerals reported to co-occur with thomsonite nodules. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCa₂Al₅Si₅O₂₀·6H₂O
- Mohs hardness
- 5-5.5
- Density
- 2.3-2.4 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Radial Fibrous Nodules
- Cleavage
- Perfect
- Rarity
- Uncommon
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Basalt Amygdules
- Typical price
- $10-50 per polished nodule, $100+ for rare specimens
Where rockhounds find thomsonite nodules
1 mapped spotsClassic worldwide localities
- Grand Marais, Minnesota, USA
- Scotland
- Nova Scotia, Canada
- Iceland
Field-hunting tip
Look in basalt amygdules country — that is the host setting where thomsonite nodules typically forms. If you start seeing calcite, quartz, prehnite in float, you are in the right ground. Field specimens usually show a radial fibrous nodules habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Minnesota — start trip planning there.
Common questions
How do you identify thomsonite nodules?+
Where is thomsonite nodules found?+
Can I find thomsonite nodules in the United States?+
How much is thomsonite nodules worth?+
What rocks look like thomsonite nodules?+
What minerals are found with thomsonite nodules?+
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Find thomsonite nodules on the map
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