Offretite is a rare zeolite mineral that forms distinctive hexagonal prismatic crystals. It is most commonly found in the vugs or cavities of volcanic basalt flows, often associated with other zeolites like levyne.
Is this offretite?
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 offretite with a known reference. Offretite sits at Mohs 4, 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, colorless.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: hexagonal, prismatic, radial.
Often found alongside offretite
Minerals reported to co-occur with offretite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KCaMg(Si₁₃Al₅)O₃₆·15H₂O
- Mohs hardness
- 4
- Density
- 2.13 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
- Crystal habit
- Hexagonal, prismatic, radial
- Cleavage
- {0001}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Lining cavities in basalt
Where rockhounds find offretite
Classic worldwide localities
- Milwaukie, Clackamas Co., at Gordon Gulch, Owyhee Dam, Malheur Co., and Ritter Hot Springs, Grant Co., Oregon, USA
- Rock Island Dam, Douglas Co., Washington, USA
- Queen Creek, 10 km west of Superior, Pinal Co., and from three km south of Horseshoe Dam, Maricopa Co., Arizona, USA
- Mont Sémiol (Mont Simiouse), Montbrison, Loire, France
- A number of localities on the Vogelsberg, Hesse, Germany
- Southwest of Westwold, British Columbia, Canada
Field-hunting tip
Where it forms: Lining cavities in basalt. If you start seeing zeolites, especially erionite, levyne in float, you are in the right ground. Typical habit: hexagonal, prismatic, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify offretite?+
Where is offretite found?+
What minerals are found with offretite?+
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Find offretite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
