Gmelinite-Ca is a member of the zeolite group often found as sharp, rhombohedral crystals in volcanic amygdules. Collectors should look for its distinctive hexagonal habit, which can sometimes appear as complex interpenetrating twins, typically occurring in basaltic environments alongside other zeolites.

Hardness

4.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineraluncommonZeolite Group family

Gmelinite-Ca

Hardness: 4.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this gmelinite-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 gmelinite-ca with a known reference. Gmelinite-Ca sits at Mohs 4.5, 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, reddish white, pink, greenish white, flesh red.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: crystalline, druse.

Often confused with

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

Often found alongside gmelinite-ca

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

All properties

Chemical formula: Ca₂(Si₈Al₄)O₂₄·11H₂O
Mohs hardness: 4.5
Density: 2.11 g/cm³
Colors: White Reddish white Pink Greenish whiteFlesh red
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Hexagonal
Crystal habit: Crystalline, druse
Cleavage: {10*0}, distinct; parting on {00*1}
Rarity: Uncommon
Uses: Collector
Host rock: Formed from calcium-rich fluids, in basalts and related igneous rocks, also pegmatites

Where rockhounds find gmelinite-ca

Classic worldwide localities

Bergen Hill, Hudson Co., and Great Notch, Paterson, and Prospect Park, Passaic Co., New Jersey, USA
Springfield, Lane Co., Oregon, USA
Montecchio Maggiore, Vicenza, Italy
Glenarm, in Co. Antrim, Ireland
Isle of Skye, Scotland
Pyrgos, Cyprus

Field-hunting tip

Where it forms: Formed from calcium-rich fluids, in basalts and related igneous rocks, also pegmatites. If you start seeing analcime, chabazite, calcite in float, you are in the right ground. Typical habit: crystalline, druse. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify gmelinite-ca?+

Mohs hardness is 4.5. Luster: vitreous. The streak is white. Common colors include white, reddish white, pink, greenish white.

Where is gmelinite-ca found?+

Notable localities include Bergen Hill, Hudson Co., and Great Notch, Paterson, and Prospect Park, Passaic Co., New Jersey, USA; Springfield, Lane Co., Oregon, USA; Montecchio Maggiore, Vicenza, Italy; Glenarm, in Co. Antrim, Ireland; Isle of Skye, Scotland.

What rocks look like gmelinite-ca?+

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

What minerals are found with gmelinite-ca?+

Gmelinite-Ca commonly co-occurs with Analcime, Chabazite, Calcite, Aragonite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

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

Where it forms: Formed from calcium-rich fluids, in basalts and related igneous rocks, also pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is gmelinite-ca used for?+

Gmelinite-Ca is used in collector.

Find gmelinite-ca on the map

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