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 1-2, 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.
- 4Match the color rangeCompare against the expected color range: white, gray, gray white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Nitrocalcite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky on Nitrocalcite and vitreous on Niter.
How to tell apart: Luster reads silky on Nitrocalcite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Luster reads silky on Nitrocalcite and vitreous, silky in fibrous aggregates on Epsomite.
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
- 1-2
- Density
- 1.90 g/cm³
- Colors
- Streak
- White
- Luster
- Silky
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Observed
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- Typically formed in caves and on alkaline soils, which may be seasonal
Where rockhounds find nitrocalcite
Classic worldwide localities
- Kartchner Caverns, near Benson, Cochise Co., Arizona, USA
- Pulo di Molfetta caves, Apulia, Italy
- Limagne, Auvergne, France
- David’s and Chaos Caves, Transvaal, South Africa
- Ludwig Cave, north Namibia
- Paddy’s River mine, Australian Capital Territory
Field-hunting tip
Where it forms: Typically formed in caves and on alkaline soils, which may be seasonal. If you start seeing niter, nitromagnesite, alunite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify nitrocalcite?+
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Find nitrocalcite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
