Gobbinsite is a rare zeolite mineral that typically forms small, white pseudocubic crystals within cavities of basaltic rocks. It is best identified through its characteristic interpenetrant twinning and association with other zeolites like phillipsite.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrareZeolite Group family

Gobbinsite

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

Is this gobbinsite?

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 gobbinsite with a known reference. Gobbinsite 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: lemon white, chalky white, light brown.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: aggregates, lath.

Often confused with

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

Often found alongside gobbinsite

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

Calcite
mineral · Mohs 3

All properties

Chemical formula: Na₅(Si₁₁Al₅)O₃₂·11H₂O
Mohs hardness: ~4
Density: 2.194 g/cm³
Colors: Lemon whiteChalky whiteLight brown
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Aggregates, lath
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral in amygdules in basalts (Co. Antrim, Ireland); in cavities in sodalite syenite in an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada)

Where rockhounds find gobbinsite

Classic worldwide localities

Island Magee, from Two Mouth Cave, at the coastal escarpment near Hills Port, south of The Gobbins, and at Dunseverick, near Giant's Causeway, Co. Antrim, Ireland
Mont Saint-Hilaire, Quebec, Canada

Field-hunting tip

Where it forms: A secondary mineral in amygdules in basalts (Co. Antrim, Ireland); in cavities in sodalite syenite in an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada). If you start seeing gmelinite, calcite, tetranatrolite in float, you are in the right ground. Typical habit: aggregates, lath. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify gobbinsite?+

Mohs hardness is ~4. Luster: vitreous. The streak is white. Common colors include lemon white, chalky white, light brown.

Where is gobbinsite found?+

Notable localities include Island Magee, from Two Mouth Cave, at the coastal escarpment near Hills Port, south of The Gobbins, and at Dunseverick, near Giant's Causeway, Co. Antrim, Ireland; Mont Saint-Hilaire, Quebec, Canada.

What rocks look like gobbinsite?+

Gobbinsite is most often confused with Phillipsite, Harmotome, Chabazite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with gobbinsite?+

Gobbinsite commonly co-occurs with Gmelinite, Calcite, Tetranatrolite, Sérandite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does gobbinsite form in?+

Where it forms: A secondary mineral in amygdules in basalts (Co. Antrim, Ireland); in cavities in sodalite syenite in an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada). Working float back to the host body is the standard way to chase a fresh occurrence.

What is gobbinsite used for?+

Gobbinsite is used in collector.

Find gobbinsite on the map

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