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

Streak

White

Transparency

Translucent

mineralrareZeolite Group family

Erionite-Ca

Hardness: 3.5-4
Luster: Vitreous
Streak: White
Transparency: Translucent

No image

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. Erionite-Ca leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Erionite-Ca typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless, yellowish.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: acicular or fibrous radial aggregates.

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: Ca₂KNa(Si₂₇Al₉)O₇₂·28H₂O
Mohs hardness: 3.5-4
Density: 2.09 g/cm³
Colors: White Colorless Yellowish
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Hexagonal
Crystal habit: Acicular or Fibrous Radial Aggregates
Cleavage: Good On {10-10}
Rarity: Rare
Uses: Collector, Scientific Research
Host rock: Volcanic Cavities and Ash Flow Tuffs
Typical price: $20-100 per specimen

Where rockhounds find erionite-ca

Classic worldwide localities

Oregon, USA
Nevada, USA
Iceland
Italy
New Zealand

Field-hunting tip

Look in volcanic cavities and ash flow tuffs country — that is the host setting where erionite-ca typically forms. If you start seeing calcite, phillipsite, chabazite in float, you are in the right ground. Field specimens usually show a acicular or fibrous radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify erionite-ca?+

Mohs hardness is 3.5-4. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless, yellowish.

Where is erionite-ca found?+

Notable localities include Oregon, USA; Nevada, USA; Iceland; Italy; New Zealand.

How much is erionite-ca worth?+

Typical asking prices fall in the range of $20-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is erionite-ca safe to handle?+

It contains toxic constituents. 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. Handle with care, avoid grinding or breathing dust, and store separately.

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?+

Erionite-Ca typically forms in volcanic cavities and ash flow tuffs. 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.