Nitrocalcite is a highly soluble nitrate mineral that typically forms as efflorescent crusts or delicate, fibrous white coatings on limestone cave walls. Due to its extreme solubility and hygroscopic nature, it must be stored in a dry, airtight container to prevent it from deliquescing into a liquid. Collectors often look for it in protected cave environments where organic matter decomposition provides the necessary nitrogen.
Is this nitrocalcite?
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 nitrocalcite with a known reference. Nitrocalcite sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Nitrocalcite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Nitrocalcite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: efflorescent crusts, acicular fibers, cotton-like aggregates.
Often confused with
Nitrocalcite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside nitrocalcite
Minerals reported to co-occur with nitrocalcite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(NO₃)₂·4H₂O
- Mohs hardness
- 1.5-2
- Density
- 1.9 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Efflorescent Crusts, Acicular Fibers, Cotton-like Aggregates
- Cleavage
- Perfect
- Rarity
- Common
- Uses
- Collector, Scientific Research
- Host rock
- Limestone Caves and Arid Soil Environments
- Typical price
- $10-30 for small vials or crust samples
Where rockhounds find nitrocalcite
Classic worldwide localities
- Mammoth Cave, Kentucky, USA
- Nitrate caves, Chile
- Italy
- Egypt
Field-hunting tip
Look in limestone caves and arid soil environments country — that is the host setting where nitrocalcite typically forms. If you start seeing niter, gypsum, halite in float, you are in the right ground. Field specimens usually show a efflorescent crusts, acicular fibers, cotton-like aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find nitrocalcite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
