An interesting specimen of green quartz on a nicely contrasting matrix of lightly iron stained calcite.  There is also a sprinkling of pyrite or chalcopyrite in some areas, with secondary growth of white calcite.

I have not seen examples of this material before-- it is quite possible that I simply haven't paid attention, but I looked on Mindat and couldn't fine more examples either.

As it seemed new to me, I pressed the person I bought it from for more information.  Apparently it was the best piece from a small lot taken to the Quartzite, AZ Show (a smaller show that coincides with Tucson) by a Mexican dealer.  In any case, it's certainly something different for the collector or quartz or Mexican minerals.

Please note that there is a bit of damage.