1) Monoclinic mineral 
Jordanite is a sulfosalt mineral with chemical formula Pb14(As,Sb)6S23 in the monoclinic crystal system, named after the German scientist Dr H. Jordan (1808–1887) who discovered it in 1864. Lead-grey in colour (frequently displaying an iridescent tarnish), its streak is black and its lustre is metallic. Jordanite has a hardness of 3 on Mohs scal...