Mordenite is a common zeolite mineral typically found in volcanic rocks as delicate, fibrous, or radiating needle-like crystal clusters. Collectors should look for its distinctive cotton-like or tufted appearances within basalt vesicles often associated with other zeolites.
Is this mordenite?
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 mordenite with a known reference. Mordenite sits at Mohs 3-4, 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, pearly on {010}, silky if fibrous.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellowish, pinkish.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: blocky, reniform, striated.
Often confused with
Mordenite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Natrolite is the harder of the two (Mohs 5-5.5 vs. 3-4).
How to tell apart: Mesolite is the harder of the two (Mohs 5 vs. 3-4).
How to tell apart: Scolecite is the harder of the two (Mohs 5-5.5 vs. 3-4).
Often found alongside mordenite
Minerals reported to co-occur with mordenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na₂,Ca,K₂)₄(Al₈Si₄₀O₉₆)·28H₂O
- Mohs hardness
- 3-4
- Density
- 2.12-2.15 g/cm³
- Streak
- White
- Luster
- Vitreous, pearly on {010}, silky if fibrous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Blocky, reniform, striated
- Cleavage
- Perfect on {100}, distinct on {010}
- Rarity
- Common
- Uses
- Collector, Industrial, Adsorbent
- Host rock
- In veins and amygdules in various igneous rocks; a hydration product of volcanic glasses; an authigenic mineral in sediments
Where rockhounds find mordenite
1 mapped spotsClassic worldwide localities
- Stevenson, Skamania Co., Washington, USA
- Challis, Custer Co., Idaho, USA
- Crooked Creek, Rome, Malheur Co., at Goble, Columbia Co., and at Cape Lookout, Tillamook Co., Oregon, USA
- Table Mountain, Jefferson Co. and in Wolf Creek Pass, Mineral Co., Colorado, USA
- Morden and along the Bay of Fundy, Nova Scotia, Canada
- San Piero in Campo, Elba, Italy
Field-hunting tip
Where it forms: In veins and amygdules in various igneous rocks; a hydration product of volcanic glasses; an authigenic mineral in sediments. If you start seeing zeolites, calcite, kaolinite in float, you are in the right ground. Typical habit: blocky, reniform, striated. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Colorado. Start trip planning there.
Common questions
How do you identify mordenite?+
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Can I find mordenite in the United States?+
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Find mordenite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
