Crystal Harvest Field Guide

Stilbite & Zeolites: The Complete Guide

The “boiling stones”: minerals riddled with molecular-size channels that grow inside old lava flows. Stilbite’s pearly bow-ties are the classic find, from Paterson, New Jersey, to the Bay of Fundy and India’s Deccan Traps.

Quick facts

“Boiling stone”From Greek zeo (to boil) and lithos (stone). Heat them and water hisses out as steam.
Built-in channelsZeolites have a 3-D aluminosilicate framework full of water-filled cavities and channels.
Molecular sievesThey can lose and regain water and swap ions without collapsing, and they sort molecules by size.
82 speciesThe 1997 international report accepted 82 zeolite species, and more have been named since.
250+ frameworksOver 250 framework structures are known, most of them synthetic. More than 40 occur in nature.
Stilbite: 3.5–4Soft, with a pearly luster and sheaf or bow-tie crystal groups.
Stilbite-Ca / -NaTwo species that look identical. The name depends on whether calcium or sodium dominates.
Provincial mineralStilbite has been Nova Scotia’s official mineral since 1999.

A short history

Zeolites went from a chemist’s curiosity to some of the most useful industrial materials on Earth.

  1. 1756Swedish mineralogist Axel Fredrik Cronstedt heats a mineral that releases steam and coins the name “zeolite.”
  2. 1792Chabazite is named.
  3. 1796René-Just Haüy names stilbite from the Greek stilbein, “to shine,” for its pearly luster.
  4. 1803Natrolite is named by Martin Klaproth.
  5. 1822Heulandite is named after collector J. H. Heuland, separating it from stilbite.
  6. 1864Mordenite is named after Morden, Nova Scotia, its type locality.
  7. 1800s–1900sThe trap-rock quarries around Paterson, New Jersey, yield some of the finest zeolite and prehnite specimens in North America.
  8. 1964Mobil puts zeolite catalysts into commercial use for cracking crude oil, transforming gasoline refining.
  9. 1997An international subcommittee standardizes zeolite names, accepting 82 species and discrediting “leonhardite.”
  10. 1999Nova Scotia adopts stilbite as its provincial mineral.
  11. 2011Zeolite sandbags are used to soak up radioactive cesium after the Fukushima accident.

How zeolites grow in lava

The classic zeolite localities are old basalt lava flows. The crystals didn’t form from the lava itself. They grew later, from warm water moving through the cooled rock.

  1. Gas bubbles. As basalt lava cools, gas bubbles leave hollows called vesicles.
  2. Warm water arrives. Long after the lava solidifies, water carrying silica, aluminum, calcium, and sodium circulates through the rock.
  3. Early, hotter minerals. At higher temperatures (roughly 270–180 °C in Deccan studies), prehnite and laumontite form first.
  4. The zeolite stage. From about 180 °C to under 100 °C, scolecite, heulandite, stilbite, and chabazite grow in the cavities.
  5. Late overgrowths. Much later and cooler, apophyllite and a second generation of chabazite can form on top.
  6. Zoning. Different species form at different depths and temperatures, so a thick lava pile shows layers of zeolite zones, a pattern first mapped by G. P. L. Walker.

More on the process: basalt’s hidden cavities.

Classic localities

Three giant lava provinces produce most of the world’s collector zeolites.

New Jersey

Watchung Mountains, Paterson

Basalt about 200 million years old from when Pangaea rifted apart. Classic stilbite, heulandite, chabazite, prehnite, and pectolite. Most historic Paterson quarries are now closed or built over. See Paterson’s quarries.

Nova Scotia

Bay of Fundy & Minas Basin

About 201-million-year-old North Mountain basalt. Beaches and cliffs at Five Islands, Two Islands, Wasson Bluff, Partridge Island, and Cape d’Or yield stilbite, chabazite, and heulandite.

India

Deccan Traps (Pune, Nashik, Mumbai)

Basalts about 66 million years old covering about 500,000 km². The world’s most prolific stilbite source, with salmon-pink stilbite on green apophyllite and giant scolecite sprays. Specimens are a by-product of construction quarrying.

Iceland

Eastern Iceland

Classic zeolite zoning in young lava piles.

Zeolite species cheat sheet

Stilbite

Sheaf or bow-tie bundles with a pearly luster. White, peach, salmon, or tan. H 3.5–4.

Heulandite

Flat, coffin-shaped crystals with a pearly face. H 3–4.

Chabazite

Near-cube-shaped rhombs, often twinned. H 3–5.

Natrolite

Slender needles and sprays. H 5–6.

Mesolite

Hair-fine white tufts. Very fragile. H 5–5.5.

Scolecite

Radiating needle sprays. The name means “worm,” from how it curls when heated. H 5–5.5.

Laumontite

Turns chalky and crumbles as it dries out. H 3.5–4.

Not zeolites: apophyllite and prehnite

Common companions but different minerals. Apophyllite is a sheet silicate, and prehnite is its own mineral. See prehnite.

Zeolites at work

Collectors love the crystals, but industry uses zeolites by the million tonnes, mostly synthetic zeolites or zeolite-rich volcanic tuff, not basalt specimens.

RefiningZeolite catalysts crack crude oil into gasoline, commercially since 1964.
DetergentsZeolites soften water in detergents, replacing phosphates.
Cat litter and odorNatural zeolites absorb moisture and odors.
Animal feedAbout 46% of US natural zeolite sales go to animal feed.
Nuclear cleanupZeolites trap radioactive cesium, and were used after Fukushima.
~1 million tonnesApproximate world natural zeolite production in 2024.

Myths vs. facts

Myth: Prehnite is a zeolite.

Fact: It is found with zeolites but is not one.

Myth: Apophyllite is a zeolite.

Fact: It is a sheet silicate that often grows with zeolites.

Myth: Zeolites formed from molten lava.

Fact: They grew later, from cooler water moving through the rock.

Myth: You can tell stilbite-Ca from stilbite-Na by eye.

Fact: They look identical and need chemical analysis.

Myth: The zeolite in detergent came from crystals like these.

Fact: Industrial zeolites are mostly synthetic or mined from zeolite-rich tuff.

Myth: Leonhardite is a mineral species.

Fact: It is just dehydrated laumontite, discredited as a species in 1997.

Myth: Indian zeolites are mined for collectors.

Fact: They are a by-product of quarrying basalt for construction, and output has dropped as quarries mechanize.

Care and display

Laumontite

Loses water in dry air within hours to days and crumbles. Store it in a humid, sealed container.

Soft crystals

Stilbite and heulandite (3.5–4) scratch easily. Handle by the matrix.

Needle zeolites

Natrolite, mesolite, and scolecite are fragile. Keep them in boxes and away from drafts and fingers.

Fibrous zeolites

Some fibrous zeolites, such as erionite, are a health hazard. Don’t dry-brush or crush fibrous specimens.

Cleaning

Gentle water rinses and air drying for sturdy pieces. Avoid heat, which drives out water.

Stilbite and zeolites in the shop

Hand holding a Nova Scotia stilbite specimen, amber zeolite crystals filling a cavity in grey basalt
Stilbite — Nova Scotia$24.60
Hand holding an elongated New Jersey specimen with a pale grey-green calcite crust over stilbite
Calcite on Stilbite — New Jersey$36.08
Nine New Jersey stilbite bowtie specimens arranged on white beside a caliper for scale
New Jersey Stilbite Crystal Lot — 9 Natural Bowtie Specimens$68.88
Four New Jersey stilbite bowtie crystal specimens arranged on white beside a caliper
New Jersey Stilbite Crystal Lot — 4 Natural Bowtie Specimens$39.36
See all stilbite

Frequently asked questions

Why are they called “boiling stones”?

Heating a zeolite drives water out of its channels as steam, so early chemists saw them seem to boil.

How do I tell stilbite from heulandite?

Stilbite forms sheaf or bow-tie bundles. Heulandite forms flat, coffin-shaped crystals.

How old are zeolite specimens?

The host basalts are about 200 million years old (New Jersey), 201 million (Nova Scotia), and 66 million (India). The zeolites grew later.

Why do so many zeolites come from India?

The Deccan Traps are enormous, and active construction quarries constantly open new cavities.

Can I collect in Paterson?

Mostly not. Historic quarries are closed, built over, private, or parkland.

Is stilbite Nova Scotia’s official mineral?

Yes, since 1999.

What is stilbite?

Stilbite is a zeolite mineral: a hydrated calcium-sodium aluminum silicate that grows inside gas bubbles and cracks in volcanic basalt. It typically forms “bowtie” or sheaf-shaped bundles of crystals in white, cream, peach, or pink, with a pearly luster on its cleavage faces. It is about 3.5 to 4 on the Mohs scale.

Is stilbite rare?

No. Stilbite is one of the most common zeolites and is found wherever basalt cavities exist. Large, colorful, well-formed specimens are less common; the best come from India’s Deccan Traps, Nova Scotia (where it is the provincial mineral), Iceland, and the trap-rock quarries of New Jersey. See our stilbite specimens.

What is zeolite good for?

Zeolites have a crystal structure full of tiny tunnels and cages, which lets them trap water and certain molecules. That makes them useful as water softeners, in laundry detergents, cat litter, odor control, gas separation (molecular sieves), and as catalysts in oil refining. Most industrial zeolites are synthetic, but natural zeolites such as clinoptilolite are also mined.

What are the benefits of stilbite crystal?

As a mineral, stilbite’s value is for collecting and display: it forms some of the most attractive crystal groups in basalt, often alongside apophyllite and other zeolites. It is popular in crystal-healing practices, but there is no scientific evidence for those effects. It is soft and can lose water, so keep it out of heat and direct sun.

Keep reading

Sources and further reading

The current number of zeolite species is higher than the 1997 count. This page cites the official 1997 figure.

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