Calclacite is a rare secondary mineral often found as an efflorescence on calcareous artifacts or limestone surfaces stored in oak cabinets. It forms delicate, needle-like white fibrous coatings or crusts resulting from the reaction between acetic acid vapors from wood and calcium-rich substrates. It is primarily a curiosity for collectors interested in the chemical reactions within museum collections.
Is this calclacite?
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 calclacite with a known reference. Calclacite 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: silky in aggregates.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular crusts, fibrous needles.
Often confused with
Calclacite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky in aggregates on Calclacite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Luster reads silky in aggregates on Calclacite and vitreous, silky in fibrous aggregates on Epsomite.
All properties
- Chemical formula
- Ca(CH₃COO)Cl·5H₂O
- Mohs hardness
- 2
- Density
- 1.5 g/cm³
- Colors
- Streak
- White
- Luster
- Silky in aggregates
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular crusts, fibrous needles
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Forms on calcareous rock and fossil specimens and pottery sherds thorough the action of acetic acid derived from oak storage cabinets
Where rockhounds find calclacite
Classic worldwide localities
- Vienna, Austria
- Rome, Italy
- London, United Kingdom
Field-hunting tip
Where it forms: Forms on calcareous rock and fossil specimens and pottery sherds thorough the action of acetic acid derived from oak storage cabinets. If you start seeing unspecified efflorescent salts in float, you are in the right ground. Typical habit: acicular crusts, fibrous needles. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify calclacite?+
Where is calclacite found?+
What rocks look like calclacite?+
What minerals are found with calclacite?+
What kind of rock does calclacite form in?+
What is calclacite used for?+
Find calclacite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
