Gonnardite is a rare zeolite mineral that frequently occurs as radiating fibrous or acicular sprays within basaltic cavities. It is visually similar to other fibrous zeolites like natrolite, and often requires advanced testing or association context to distinguish it in the field.
Is this gonnardite?
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 gonnardite with a known reference. Gonnardite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: fibrous, spherical.
Often confused with
Gonnardite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky on Gonnardite and vitreous, silky when fibrous on Mesolite.
How to tell apart: Luster reads silky on Gonnardite and vitreous to pearly on Natrolite.
How to tell apart: Luster reads silky on Gonnardite and vitreous on Thomsonite.
Often found alongside gonnardite
Minerals reported to co-occur with gonnardite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂CaAl₄Si₆O₂₀·7H₂O
- Mohs hardness
- 5
- Density
- 2.25-2.36 g/cm³
- Colors
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Fibrous, spherical
- Cleavage
- Perfect
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In cavities in basalt, leucite tephrite, and altered skarn
Where rockhounds find gonnardite
Classic worldwide localities
- Crestmore, Riverside Co., California, and around Honolulu, Oahu, Hawaii, USA
- Chaux de Bergonne, Gignat, Puy de Dôme, France
- Capo di Bove, near Rome, Lazio, Italy
- Aci Castello, Aci Trezza, Osilo, Italy
- Arendal, Tvedalen, at Brevik, around the Langesundsfjord, Norway
- Klöch, Styria, Austria
Field-hunting tip
Where it forms: In cavities in basalt, leucite tephrite, and altered skarn. If you start seeing zeolites, calcite in float, you are in the right ground. Typical habit: fibrous, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gonnardite?+
Where is gonnardite found?+
What rocks look like gonnardite?+
What minerals are found with gonnardite?+
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Find gonnardite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
