:Locality: María Josefa Mine, El Madroñal, Rodalquilar, Andalusia, Spain Size: 3.6 × 3.4 × 2.2 cm Description: In this specimen we have different arsenates. Colorless cubic crystals are natropharmacoalumite, accompanied by yellowish natropharmacosiderite. In some crystals you can observe a yellowish crystal core with colorless external part of both species. Small lemon yellow crytals has been identified as pharmacoalumite. The name of natropharmacoalumite is in allusion to the cation dominance of Na and Al. — Photo: Joan Rosell , from rosellminerals.com · CC BY-SA 4.0
Natropharmacoalumite
Natropharmacoalumite is an IMA-recognized mineral species in the arsenate class, with the chemical formula NaAl₄(AsO₄)₃(OH)₄·4H₂O.
It crystallizes in the cubic crystal system (space group P-43m). It is a member of the Pharmacosiderite structural group.
Key properties: Mohs hardness 2.5; specific gravity 2.564; White streak; Vitreous to adamantine luster.
IMA symbol Npal, IMA status: approved, named in 2010.
Found as a secondary mineral in cavities and fractures in quartz in an epithermal gold-bearing alunite deposit.
It is found associated with Quartz, chenevixite, kaolinite, jarosite, indeterminate Fe and Sb oxyhydroxides.
As the Na (natro) and Al (alum) end-member in the pharmacosiderite supergroup.