Dims: 2.73x1.74x1.42" (6.93x4.43x3.61cm)
Wt: 6.41oz (181.7g)
Nica, Chihuahua, Mexico
This specimen is primarily composed of bournotite with all of the surface crystals showing excellent (but not twinned) crystallization. The bournonite is black and opaque, with a vitreous luster. The crystals display a hex-octagonal form - all of the faces are triangles. Some faces show stepped growth patterns, and only a few show strong striations. The lack of twinning means that I cannot see any "cog wheel" crystals. The bournonite is accompanied by tiny quartz crystals, some doubly terminated, and by very nice arsenopyrite crystals which a loupe resolves as golden prismatic crystals with a diamond cross section and a slanted termination. There is also a small amount of albite present with good crystal form.