Panasqueira Mines, Covilhã, Castelo Branco, Portugal

FeAsS

Crystal System: monoclinic
Colour: silver-white to steel-gray, may have a slight yellow appearance
Lustre: metallic, sub-metallic
Habitus: tabular to blocky, pseudo-octahedral to prismatic crystals, sometimes twinned
Hardness:  5½ - 6
Fracture: irregular/uneven
Cleavage: distinct/good distinct on {001}; {010} less distinct
Density: 6.18 g/cm³ 
Origin and geological occurrence: it is often mined, together with other metallic minerals, from veins that might contain gold, silver, lead, tungsten, or tin. In these deposits arsenopyrite usually occurs in a granular massive form. Arsenopyrite has also been mined from sulfide deposits formed by contact metamorphism.

Mindat link
Smorf link 

Samples:

As Arsenopirite Grey compact masses. #economic minerals