Franzinite is a rare member of the cancrinite group, typically found as small, prismatic crystals within volcanic ejecta blocks. It is primarily known for its occurrences at the Pitigliano locality in Italy, where it forms in association with other rare silicates.
Is this franzinite?
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 franzinite with a known reference. Franzinite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: pearl white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: prismatic.
Often confused with
Franzinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads pearly on Franzinite and vitreous, pearly, or greasy on Cancrinite.
How to tell apart: Vesuvianite is the harder of the two (Mohs 6-7 vs. 5); luster reads pearly on Franzinite and vitreous to resinous on Vesuvianite.
How to tell apart: Luster reads pearly on Franzinite and vitreous to greasy on Nepheline.
Often found alongside franzinite
Minerals reported to co-occur with franzinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,K)₃₀Ca₁₀(Si₃₀Al₃₀)O₁₂₀(SO₄)₁₀·2H₂O
- Mohs hardness
- 5
- Density
- 2.46-2.52 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent to opaque
- Crystal system
- Trigonal
- Crystal habit
- Prismatic
- Cleavage
- {0001}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In ejected metasomatized pumice blocks, thought to be the product of a syntectic process between a trachytic magma and carbonate rocks at the volcanic vent
Where rockhounds find franzinite
Classic worldwide localities
- Pitigliano quarry, near Grosseto, Tuscany, Italy
- Sacrofano and Ariccia, near Rome, Lazio, Italy
Field-hunting tip
Where it forms: In ejected metasomatized pumice blocks, thought to be the product of a syntectic process between a trachytic magma and carbonate rocks at the volcanic vent. If you start seeing diopside, vesuvianite, afghanite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find franzinite on the map
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