Xonotlite , Epidote-(Pb) (formerly known as Hancockite ) Locality: Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA Acicular crystals of xonotlite with hancockite. Field of view 3 mm. Photo and specimen Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Hancockite
Hancockite is an IMA-recognized mineral species in the silicate class, with the chemical formula CaPb(Al₂Fe³⁺)[Si₂O₇][SiO₄]O(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/m). It is a member of the Clinozoisite, Epidote structural group.
Key properties: Mohs hardness 6–7; specific gravity 4.03; Vitreous luster; optically biaxial.
IMA symbol Hnc, IMA status: approved, named in 1899.
Found in a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA); in a metamorphosed manganese-iron orebody in skarns enclosed in dolomitic marble (Jakobsberg, Sweden).
It is found associated with Andradite, franklinite, manganaxinite, clinohedrite, roeblingite, datolite, prehnite, willemite, barite, hendricksite, barian feldspar, phlogopite, lead.
The name refers to Elwood P. Hancock (1836–1916), of Burlington, New Jersey, USA, collector of minerals from Franklin.