Beige crystal group of the extremely rare phosphate mineral francoanellite from the TL In Italy (Grotta di Castellana, Bari, Apulia, Italy). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Francoanellite
Francoanellite is an IMA-recognized mineral species in the phosphate class, with the chemical formula K₃Al₅(PO₃OH)₆(PO₄)₂·12H₂O.
It crystallizes in the hexagonal crystal system (space group R-3c).
Key properties: specific gravity 2.26; optically uniaxial.
IMA symbol Fan, IMA status: approved, named in 1974.
An alteration product probably formed by reaction between bat guano and clay minerals (Castellana Cave, Italy); in soils developed on granite debris and bat guano mixtures.
It is found associated with Taranakite (Castellana Cave, Italy); taranakite, hydroxylapatite, brushite (Little Swallow Cave, Italy); alunite, aragonite, berlinite, collophane.
The mineral was named to honor Franco Anelli, formerly Professor of Geography, University of Bari, Bari, Italy, who found the Castellana caves.