Self-collected tri-color nitrocalcite specimen. Collection of Dennis Tryon. Locality: Gila River, Winkelman area, Gila & Pinal Cos., Arizona, USA Dimensions: 5 cm x 2.5 cm x 2 cm. — Photo: Dennis Tryon · CC0
Nitrocalcite
Natural calcium nitrate — a deliquescent mineral of cave walls and arid soils.
Intro adapted from Wikipedia (CC BY-SA).
Nitrocalcite is an IMA-recognized mineral species in the nitrate class, with the chemical formula Ca(NO₃)₂·4H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c).
Key properties: specific gravity 1.9; Silky luster; optically biaxial.
IMA symbol Ncal, grandfathered status — known before the IMA’s founding, named in 1783.
Typically formed in caves and on alkaline soils, which may be seasonal.
It is found associated with Niter, nitromagnesite (caves); alunite, aragonite, berlinite, collophane, crandallite, francoanellite, gypsum, huntite, hydromagnesite, leucophosphite.
The name refers to NITROgen and CALCium in the composition.