Gismondine-Ca is a member of the zeolite group characterized by its striking pseudo-tetragonal, cruciform twinning habits. It is typically found lining vesicles in volcanic rocks, particularly in association with other zeolites and calcite. Collectors value it for its complex crystal structure and rarity compared to more common zeolite species.
Is this gismondine-ca?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch gismondine-ca with a known reference. Gismondine-Ca sits at Mohs 4-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Gismondine-Ca leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Gismondine-Ca typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: pseudo-tetragonal bipyramidal crystals, often in complex cruciform twinned clusters.
Often confused with
Gismondine-Ca vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside gismondine-ca
Minerals reported to co-occur with gismondine-ca. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl₂Si₂O₈·4H₂O
- Mohs hardness
- 4-5
- Density
- 2.26 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Pseudo-tetragonal Bipyramidal Crystals, Often in Complex Cruciform Twinned Clusters
- Cleavage
- Distinct On {110}
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Cavities in Basaltic Volcanic Rocks and Nephelinite
- Typical price
- $10-50 per specimen depending on crystal quality
Where rockhounds find gismondine-ca
Classic worldwide localities
- Capo di Bove, Italy
- Vesuvius, Italy
- Giessen, Germany
- Antrim, Northern Ireland
Field-hunting tip
Look in cavities in basaltic volcanic rocks and nephelinite country — that is the host setting where gismondine-ca typically forms. If you start seeing phillipsite, gismondine-sr, calcite in float, you are in the right ground. Field specimens usually show a pseudo-tetragonal bipyramidal crystals, often in complex cruciform twinned clusters habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gismondine-ca?+
Where is gismondine-ca found?+
How much is gismondine-ca worth?+
What rocks look like gismondine-ca?+
What minerals are found with gismondine-ca?+
What kind of rock does gismondine-ca form in?+
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Find gismondine-ca on the map
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