Heulandite-K is a distinct member of the zeolite group often recognized by its characteristic coffin-shaped monoclinic crystals. It is typically found lining cavities in volcanic basalt and is highly prized by collectors for its aesthetic formation and crystal clarity.
Is this heulandite-k?
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 heulandite-k with a known reference. Heulandite-K sits at Mohs 3-3.5, 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 to pearly.
- 4Match the color rangeCompare against the expected color range: white, reddish white, grayish white, brownish white, yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crystalline, tabular.
Often confused with
Heulandite-K vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside heulandite-k
Minerals reported to co-occur with heulandite-k. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (K,Na,Ca)₅Al₅(Si,Al)₁₇O₄₄·18H₂O
- Mohs hardness
- 3-3.5
- Density
- 2.2 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Crystalline, tabular
- Cleavage
- Perfect on {010}
- Rarity
- Uncommon
- Uses
- Collector, Decorative
- Host rock
- Low temperature zeolite found in a wide variety of geologic environments: volcanic rocks, metamorphic rocks, pegmatites, tuffs, and deep-sea sediments
Where rockhounds find heulandite-k
Classic worldwide localities
- Albero Bassi, Vicenza, Italy (type locality)
Field-hunting tip
Where it forms: Low temperature zeolite found in a wide variety of geologic environments: volcanic rocks, metamorphic rocks, pegmatites, tuffs, and deep-sea sediments. If you start seeing stilbite, apophyllite, calcite in float, you are in the right ground. Typical habit: crystalline, tabular. Train your eye for that shape before scanning the outcrop.
More heulandite-k photos
Common questions
How do you identify heulandite-k?+
Where is heulandite-k found?+
What rocks look like heulandite-k?+
What minerals are found with heulandite-k?+
What kind of rock does heulandite-k form in?+
What is heulandite-k used for?+
Find heulandite-k on the map
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