Orange brown microcrystals of the extremely rare Ca-Fe arsenate mineral wallkilldellite-(Fe) from the type locality in Roua mine (Daluis, Alpes-Maritimes, Provence-Alpes-Cote d'Azur, France), and one of the only 5 localities known worldwide. Much rarer than the Mn term, from the elusive type locality hidden in a canyon in the Southern French Alps. Ex Dr.Hartel collection, Ex Ch.Rewitzer collection. — Photo: David Hospital · CC BY-SA 4.0
Wallkilldellite
Wallkilldellite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₂Mn²⁺₃(AsO₄)₂(OH)₄·9H₂O.
Key properties: Mohs hardness 3; specific gravity 2.85; Pale orange streak; Vitreous on cleavage surfaces; slightly resinous on fracture surfaces luster; optically uniaxial.
IMA symbol Wlk, IMA status: approved, named in 1982.
Extremely rare in massive granular franklinite-willemite ore from a metamorphosed stratiform zinc orebody (Sterling Hill).
It is found associated with Manganoan cuprian adamite, franklinite, willemite, calcite (Sterling Hill); coralloite, manganohörnesite, rhodochrosite, sarkinite, sterlinghillite.
The name refers to the dell of the Wallkill River, in which both the Sterling Hill and the Franklin deposits were discovered.