A thomsonite nodule is a zeolite-group mineral most commonly found in amygdaloidal basalt, occurring as radiating fibrous aggregates that build a colorful, banded nodule. Collectors prize it for concentric patterning and chatoyancy when cut and polished.
Is this thomsonite nodule?
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 nodule with a known reference. Thomsonite Nodule 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 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 Nodule vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside thomsonite nodule
Minerals reported to co-occur with thomsonite nodule. 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
Where rockhounds find thomsonite nodule
1 mapped spotsClassic worldwide localities
- Grand Marais, Minnesota, USA
- Scotland
- Nova Scotia, Canada
- Iceland
Field-hunting tip
Where it forms: basalt amygdules. If you start seeing calcite, quartz, prehnite in float, you are in the right ground. Typical habit: radial fibrous nodules. 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.
More thomsonite nodule photos
Common questions
How do you identify thomsonite nodule?+
Where is thomsonite nodule found?+
Can I find thomsonite nodule in the United States?+
What rocks look like thomsonite nodule?+
What minerals are found with thomsonite nodule?+
What kind of rock does thomsonite nodule form in?+
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Find thomsonite nodule on the map
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