Dims: 0.89x0.88x0.88" (2.27x2.24x2.23cm)
Wt: p.94oz (26.6g)
Mercedes Mine, Huanuco, Peru
This is essentially a large single crystal of bournonite, the "cog wheel ore". It does display the deep striations which (when combined with twinning) results in the cog-wheel shape. This specimen has a lead-gray color and a somewhat unusual luster: it is both highly lustrous and deeply pitted, which gives it an unusual texture. Most of the crystals are doubly-terminated, although these are generally obscured or distorted. There are a lot of tiny quartz crystals at one end, and a loupe reveals that there are bits of the original dull gray host rock still lingering in the crevices - it looks like the mineral was dissolved with acid. This specimen was part of an old collection.