Cowlesite is a rare calcium-rich zeolite mineral often found as tiny, white, platy or lath-like crystals in basaltic cavities. Collectors look for its distinctive radiating sprays often associated with other zeolites like thomsonite and mesolite.
Is this cowlesite?
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 cowlesite with a known reference. Cowlesite 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: pearly.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: bladed, stellate.
Often confused with
Cowlesite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Cowlesite is noticeably harder (Mohs 5-5.5 vs. 3.5-4); luster reads pearly on Cowlesite and vitreous, pearly on {010} on Heulandite.
How to tell apart: Cowlesite is noticeably harder (Mohs 5-5.5 vs. 3.5-4); luster reads pearly on Cowlesite and vitreous on Stilbite.
How to tell apart: Luster reads pearly on Cowlesite and vitreous on Thomsonite.
Often found alongside cowlesite
Minerals reported to co-occur with cowlesite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl₂Si₃O₁₀·6H₂O
- Mohs hardness
- 5-5.5
- Density
- 2.14 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Bladed, stellate
- Cleavage
- {010}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In cavities in basalts and scoria, typically the only zeolite within a single vesicle
Where rockhounds find cowlesite
Classic worldwide localities
- Goble, Columbia Co., at Beech Creek, Grant Co., and at Spray, Wheeler Co., Oregon, USA
- Capitol Peak, Thurston Co., Washington, USA
- Eight km south of Superior, Pinal Co., Arizona, USA
- Table Mountain, Jefferson Co., Colorado, USA
- Monte Lake, British Columbia, Canada
- Dunseverick, Ballyclare, in Co. Antrim, Ireland
Field-hunting tip
Where it forms: In cavities in basalts and scoria, typically the only zeolite within a single vesicle. If you start seeing zeolites, apophyllite in float, you are in the right ground. Typical habit: bladed, stellate. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cowlesite?+
Where is cowlesite found?+
What rocks look like cowlesite?+
What minerals are found with cowlesite?+
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Find cowlesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
