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. Calclacite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Calclacite typically shows a silky luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular crusts, fibrous needles.
Often confused with
Calclacite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside calclacite
Minerals reported to co-occur with calclacite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(CH₃COO)Cl·5H₂O
- Mohs hardness
- 2
- Density
- 1.74 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular Crusts, Fibrous Needles
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Anthropogenic Settings
- Typical price
- $20-100 per specimen
Where rockhounds find calclacite
Classic worldwide localities
- Vienna, Austria
- Rome, Italy
- London, United Kingdom
Field-hunting tip
Look in anthropogenic settings country, the host setting where calclacite typically forms. If you start seeing calcite, halite in float, you are in the right ground. Field specimens usually show a acicular crusts, fibrous needles habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find calclacite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
