Mineral name:  Endlichite
Chemical formula:  Pb5((V,As)O4)3Cl
Location: Sierra de Los Lamentos, Chihuahua, Mexico 
Crystal system and class:  Hexagonal? 6/m?
Genesis:  Endlichite is a rare secondary mineral formed through the oxidation of primary lead minerals (galena).  It precipitates from aqueous solutions in veins and solution cavities, along with other secondary lead minerals.
Width x length of specimen in field of view in cm:
  5 x 7
Specimen number: 
B187