Zaccagnaite is a rare zinc-aluminum layered double hydroxide mineral that typically forms thin, translucent, hexagonal tabular crystals. It is most frequently identified in museum-grade specimens from marble quarries where it occurs as delicate clusters or coatings associated with zinc-bearing mineralization.
Is this zaccagnaite?
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 zaccagnaite with a known reference. Zaccagnaite sits at Mohs 2, 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: subvitreous to adamantine.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: hexagonal, microscopic crystals, prismatic.
Often confused with
Zaccagnaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads subvitreous to adamantine on Zaccagnaite and satiny to greasy or waxy on Hydrotalcite.
How to tell apart: Streak differs, so Zaccagnaite leaves white, Woodwardite leaves light blue; luster reads subvitreous to adamantine on Zaccagnaite and pearly on Woodwardite.
How to tell apart: Luster reads subvitreous to adamantine on Zaccagnaite and pearly on Meixnerite.
Often found alongside zaccagnaite
Minerals reported to co-occur with zaccagnaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₄Al₂(OH)₁₂(CO₃)·3H₂O
- Mohs hardness
- 2
- Density
- 2.82 g/cm³
- Streak
- White
- Luster
- Subvitreous to adamantine
- Transparency
- Transparent to milky
- Crystal system
- Hexagonal
- Crystal habit
- Hexagonal, microscopic crystals, prismatic
- Cleavage
- Perfect on {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In cavities in calcite veins in marble formed through alteration of sphalerite by aluminum-rich hydrothermal fluids (Italy)
Where rockhounds find zaccagnaite
Classic worldwide localities
- Calagio quarry, Colonnata valley, Apuan Alps, Italy
- El Soplao cave, northern Spain
Field-hunting tip
Where it forms: In cavities in calcite veins in marble formed through alteration of sphalerite by aluminum-rich hydrothermal fluids (Italy). If you start seeing hydrozincite, fraipontite in float, you are in the right ground. Typical habit: hexagonal, microscopic crystals, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find zaccagnaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
