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Heulandite: The Coffin-Shaped Zeolite

By Digital Towns Crystals · Last reviewed October 8, 2026

Short answer: heulandite is a calcium-rich zeolite that grows in basalt cavities as flat, tabular crystals with a wide middle and tapered ends, a shape collectors call "coffin". It is soft (roughly 3 to 4 Mohs), light (specific gravity near 2.2) and pearly on its broad face. In the trade it is most often the green, cream or salmon base layer under apophyllite and stilbite on specimens from Nashik and Pune, India.

What does heulandite look like?

Shape is the whole story with heulandite. Minerals.net describes the crystals as usually tabular, often in a distinctive form reminiscent of old coffins, with a wider center, narrower edges, and flat top and bottom. Lay a single crystal flat and you see a six-sided slab that bulges at the shoulders and narrows toward each end. Stand a group of them on edge and they look like a row of books, often fanned slightly into curved stacks.

The broad flat face is the cleavage plane, and that is where the pearly sheen shows. The narrow edges are glassier. On a well-lit shelf a heulandite plate catches light on the broad faces only, so turning the specimen a few degrees makes whole crystals switch from dull to bright. That flicker is a decent field clue.

Heulandite also comes in less obvious habits: barrel shapes, saddle-shaped crusts, rosettes and the crystalline linings that coat entire cavity walls. On Indian specimens it is very often the drusy or blocky crust that everything else sits on, so it gets overlooked in titles even when it makes up most of the visible crystal.

How do you tell heulandite from stilbite?

They share cavities, colors and almost the same hardness, so the test is form, not color. Our stilbite guide covers the bow-tie side of the pair; the short version is below, and the planned stilbite vs heulandite comparison goes further.

Clue Heulandite Stilbite
Crystal outline Single slabs with tapered "coffin" ends Bundles of thin blades pinched at the waist
Arrangement Parallel stacks, crusts, curved books Sheaves, bow ties, balls
Where on a specimen Often the base layer or crust Usually sits on top as separate sheaves
Specific gravity about 2.2 about 2.15

If you can find one crystal with clean edges, count its outline. Heulandite shows a flat slab with angled shoulders; stilbite shows blades that never stand alone. Apophyllite, the third mineral on most of these pieces, is glassier and harder and forms near-cubes or square pyramids, so it is rarely the source of confusion.

What is heulandite made of?

Like every zeolite, heulandite is an aluminosilicate framework full of channels that hold water and loosely bound cations. Webmineral gives the formula of the common species as (Ca,Na)2-3Al3(Al,Si)2Si13O36 with 12 water molecules, a calculated specific gravity of 2.20 and a hardness of 3 to 3.5; Minerals.net lists 3.5 to 4. Treat it as a mineral a steel blade will scratch.

"Heulandite" is a series name rather than one species. The IMA zeolite subcommittee reorganized it in 1997 according to which cation dominates the channels, and Minerals.net notes that a new barium-dominating heulandite was classified in 2002. The IZA Commission on Natural Zeolites states that heulandite-Ca is by far the most common species and occurs in host rocks that are silica saturated. Essentially every heulandite in the specimen market is heulandite-Ca.

Species Dominant cation How often you will see it
Heulandite-Ca Calcium Almost every collector specimen
Heulandite-Na Sodium Uncommon, for example Challis, Idaho
Heulandite-K Potassium One locality in Vicenza, Italy
Heulandite-Sr Strontium A single Italian copper deposit
Heulandite-Ba Barium Kongsberg district, Norway

A brief history note: the IZA datasheet records that heulandite was first described by Brooke (1822), who separated it from a group of platy zeolites that had been lumped together as foliated zeolite. The name honors John Henry Heuland (1778 to 1856), an English collector and dealer. The designated type example of heulandite-Ca is from the Faeroe Islands.

Why is some Indian heulandite green?

Pure heulandite is colorless to white. The colors in the trade come from what it trapped while growing:

  • Dark green. Minerals.net reports that the Shakur Quarry in Nasik is especially known for its dark green heulandite, colored by inclusions of celadonite, a green mica-like clay. Webmineral pictures a specimen from Malagaon, India, with a green color due to chlorite inclusions. Either way the green is a coating or inclusion, not the mineral's own color, and it often concentrates near the base of each crystal.
  • Salmon, red and orange. Warm tones are usually iron-bearing inclusions or surface films. Red heulandite from Jalgaon district and orange plates from Gunnedah in New South Wales are both established collector types.
  • Cream and white. The uncolored norm, common at nearly every locality.

On the Nashik "apophyllite with stilbite on heulandite" pieces, the green layer underneath is the heulandite. Sellers often price the apophyllite and stilbite and mention the heulandite only in passing, so a strong green base is a value point a careful buyer can spot.

How and where does heulandite form?

Heulandite is a low-temperature mineral. Webmineral calls it a low temperature zeolite found in a wide variety of geologic environments: volcanic rocks, metamorphic rocks, pegmatites, tuffs, and deep-sea sediments. In lava sequences it grows from warm groundwater percolating through gas cavities long after the rock has frozen.

Iceland gives the best numbers. The IZA datasheet summarizes mapping in eastern Iceland showing that zeolite zones cut across lava flows, which means the zones were formed long after eruption and cooling of the lavas. Observations in Icelandic geothermal fields indicate that heulandite probably forms at temperatures less than 90 °C. That is warm tap-water territory, which is why heulandite and its neighbors are so easily dehydrated by heat in a collection.

The classic localities, per IZA, include Teigarhorn in Berufjord, Iceland; the Faeroe Islands; Nasik and Pune, India; Cape Blomidon, Nova Scotia; the Val di Fassa in Italy; and Paterson, New Jersey. In a study of the Deccan basalt between Nasik and Pune summarized by Turnstone Geological Services, heulandite was the most frequently encountered mineral of all, ahead of stilbite, mordenite and apophyllite. Outside India, Minerals.net singles out highly lustrous pink to peach heulandite with mordenite from the Rats Nest claim near Challis, Idaho.

Heulandite is also an industrial mineral in the broad sense. The U.S. Geological Survey counts it among the most common natural zeolites, alongside clinoptilolite, its higher-silica sibling with the same framework. Commercial deposits are fine-grained altered volcanic ash, nothing like the crystals in a specimen cabinet.

How should heulandite be cared for?

Heulandite has one perfect cleavage parallel to its broad face, so crystals split into thin sheets if knocked on edge. The tapered ends chip easily, and crusts can lift from the basalt if the matrix is flexed. Keep specimens out of direct heat, including display lights that run hot, because the channel water starts leaving well below boiling and leaves the surface white and crazed. Dust with a soft brush or a blower. Avoid soaking: water will not dissolve heulandite, but it can carry clay from the matrix into cleavage cracks and leave a tide line on green pieces. The apophyllite guide covers handling of these mixed Deccan plates.

Heulandite in crystal traditions

In crystal traditions, heulandite is associated with ancient wisdom and with travel. That is folklore, offered here as cultural context only; nothing in the mineral's chemistry bears on it.

Choosing a heulandite specimen

Look for crystals that show the coffin outline on at least some edges, a green or warm color that is even rather than patchy, and a base that is firmly attached to the basalt. Check the listed dimensions against the weight; a dense plate that is mostly matrix weighs far more for its size than a crystal-covered one. Good current examples:

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Frequently asked questions

Is heulandite rare?

No. Heulandite is among the most common zeolites, and in the Deccan basalt it is the single most frequently found cavity mineral. What is scarce is large, sharp, well-colored crystals with clean coffin outlines. Most heulandite reaches buyers as the supporting crust on apophyllite and stilbite specimens rather than as a named star.

What is the difference between heulandite and clinoptilolite?

They share the same crystal framework. Clinoptilolite is richer in silicon and alkalis and is the zeolite of commercial ash deposits, while heulandite-Ca is the calcium-rich form that grows as collector crystals in basalt. Some mineralogists treat clinoptilolite as a variety of heulandite, although the IMA keeps both names.

Why is my heulandite green on one side only?

The green usually comes from celadonite or chlorite that coated the cavity wall before or during growth. Crystals pick up more of it near their base, where they touched the wall, so the color fades toward the free tips. That uneven green is natural and is not a sign of dye.

Can heulandite be cleaned in water?

A brief rinse will not dissolve it, but soaking is a bad idea. Water can draw clay from the basalt into the cleavage cracks and leave stains, especially on green material. Use a soft brush and compressed air, and keep the specimen away from heat sources that could dry out its channel water.

How hard is heulandite?

References give roughly 3 to 4 on the Mohs scale, so a knife blade scratches it and it is softer than the apophyllite often sitting on it. The perfect cleavage makes it more fragile than its hardness suggests, and the thin tapered crystal ends chip easily.

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