Geocronite

Geocronite is a mineral, a mixed sulfosalt containing lead, antimony, and arsenic with a formula of Pb₁₄(Sb, As)₆S₂₃. Geocronite is the antimony-rich endmember of a solid solution series. The arsenic-rich endmember is named jordanite. It occurs as grey, black, to silvery white monoclinic crystals. It is found in hydrothermal veins usually associated with other similar minerals, particularly the sulfides of iron and copper.

Geocronite
General
Category	Sulfosalt minerals
Formula	Pb14(Sb, As)6S23
IMA symbol	Geo[1]
Strunz classification	2.JB.30a
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m

The mineral has been found in Spain, Ireland and Sweden where it was first identified in 1839.