Erionite-Ca is a rare fibrous zeolite that typically forms delicate, needle-like crystals in volcanic rocks. It is most famous for its link to serious respiratory health issues in regions where erionite-rich dust is present, making it a mineral of extreme interest for both its geological occurrence and its biological hazards.

Hardness

3.5-4

Mohs

Luster

Vitreous to silky

Streak

White

Transparency

Transparent

mineralrareZeolite Group family

Erionite-Ca

Hardness: 3.5-4
Luster: Vitreous to silky
Streak: White
Transparency: Transparent

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Is this erionite-ca?

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 erionite-ca with a known reference. Erionite-Ca sits at Mohs 3.5-4, 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 to silky.
4
Match the color range
Compare against the expected color range: white, green, gray, orange.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: acicular.

Often confused with

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

Often found alongside erionite-ca

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

All properties

Chemical formula: Ca₅(Si₂₆Al₁₀O₇₂)·30H₂O
Mohs hardness: 3.5-4
Density: 2.09-2.13 g/cm³
Colors: White Green Gray Orange
Streak: White
Luster: Vitreous to silky
Transparency: Transparent
Crystal system: Hexagonal
Crystal habit: Acicular
Cleavage: Distinct on {010}
Rarity: Rare
Uses: Collector, Scientific research
Host rock: Occurs in volcanic and sedimentary rocks

Where rockhounds find erionite-ca

Classic worldwide localities

Maze, Niigata Prefecture, Japan (type locality)

Field-hunting tip

Where it forms: Occurs in volcanic and sedimentary rocks. If you start seeing calcite, phillipsite, chabazite in float, you are in the right ground. Typical habit: acicular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify erionite-ca?+

Mohs hardness is 3.5-4. Luster: vitreous to silky. The streak is white. Common colors include white, green, gray, orange.

Where is erionite-ca found?+

Notable localities include Maze, Niigata Prefecture, Japan (type locality).

Is erionite-ca safe to handle?+

Erionite-Ca contains asbestiform fibers and calls for real care. Erionite is a fibrous zeolite known to be carcinogenic when inhaled, similar to asbestos. Handle with extreme care, use appropriate dust protection, and keep in a sealed container.

What rocks look like erionite-ca?+

Erionite-Ca is most often confused with Offretite, Mordenite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with erionite-ca?+

Erionite-Ca commonly co-occurs with Calcite, Phillipsite, Chabazite, Heulandite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does erionite-ca form in?+

Where it forms: Occurs in volcanic and sedimentary rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is erionite-ca used for?+

Erionite-Ca is used in collector, scientific research.

Find erionite-ca on the map

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