Epistilbite is a zeolite mineral known for its distinctive twinned, blade-like prismatic crystals. It is most easily recognized by its heart-shaped or V-shaped twinning and its occurrence in volcanic vugs alongside other zeolites.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineraluncommonZeolite Group family

Epistilbite

Hardness: 4
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this epistilbite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch epistilbite with a known reference. Epistilbite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: white, yellowish white, reddish white, brownish white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic, spherical, twinning common.

Often confused with

Epistilbite vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside epistilbite

Minerals reported to co-occur with epistilbite. Spotting these in float or country rock is a strong cue you are in the right ground.

Quartz
mineral · Mohs 7

All properties

Chemical formula: Ca₃(Si₁₈Al₆)O₄₈·16H₂O
Mohs hardness: 4
Density: 2.22-2.28 g/cm³
Colors: White Yellowish white Reddish white Brownish white
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Monoclinic
Crystal habit: Prismatic, spherical, twinning common
Cleavage: {010}, perfect
Rarity: Uncommon
Uses: Collector, Scientific research
Host rock: In cavities in basalts and gneisses

Where rockhounds find epistilbite

Classic worldwide localities

Kosmos, near Morton, Lewis Co., Washington, USA
Goble, Columbia Co., Oregon, USA
Berufjord, Iceland
Found near San Piero in Campo, Elba, Italy
Giebelsbach, near Fiesch, Valais, Switzerland
Kuroiwa, Niigata Prefecture, Japan

Field-hunting tip

Where it forms: In cavities in basalts and gneisses. If you start seeing zeolites, quartz in float, you are in the right ground. Typical habit: prismatic, spherical, twinning common. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify epistilbite?+

Mohs hardness is 4. Luster: vitreous. The streak is white. Common colors include white, yellowish white, reddish white, brownish white.

Where is epistilbite found?+

Notable localities include Kosmos, near Morton, Lewis Co., Washington, USA; Goble, Columbia Co., Oregon, USA; Berufjord, Iceland; Found near San Piero in Campo, Elba, Italy; Giebelsbach, near Fiesch, Valais, Switzerland.

What rocks look like epistilbite?+

Epistilbite is most often confused with Heulandite, Stilbite, Laumontite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with epistilbite?+

Epistilbite commonly co-occurs with Zeolites, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does epistilbite form in?+

Where it forms: In cavities in basalts and gneisses. Working float back to the host body is the standard way to chase a fresh occurrence.

What is epistilbite used for?+

Epistilbite is used in collector, scientific research.

Find epistilbite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.