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 — that is 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.
