[Rockhounds] treatment of chalcopyrite/bornite

[Rock Currier]

Jim,

The material tha you refer to as: "are mainstays of bulk specimen
dealers" are almost always chunks of massive chalcopyrite or rocks rich in
chalcopyrite (most commonly associated with pyrite). These are treated with
concentrated sulfuric and phosphoric acid to slightly oxidize? the freshly
broken chalcopyrite surfaces to give the peacock color that is so appealing
to collectors and the general public. If you repeat your request on the
Mindat general bulletin board you may be able to get some specific
formulations of how much of which acid(s) and what concentrations, but
probably not. The reason for this is two fold. The first reason is that the
guys that do this commercially are not anxious to share their secrets and
risk breaking their rice bowl and secondly, sulfuric and phosphoric acid are
strong acids and if you don't know how to handle them you could hurt
yourself and decide to sue someone.

    I have been told several times by guys that treat massive
chalcopyrite/pyrite chunks and by guys who color pyrite dollars that the
acids are fairly concentrated and you just dip the material to be treated
into it for a few minutes and pull it out and wash it off. They all indicate
that the process is something of a black art in that the results vary from
day to day and depending on where the rough rock is from. I was told by one
person who treated a lot of pyrite dollars that sometimes bucket after
bucket of pyrite dollars would come out beautifully and some days the
process didn't work at all. It probably has something to do with the
temperature of the solution and the rocks and perhaps even the humidity and
how long you let the material sit with the acid on it before washing it off.
He said you had to keep your eye on the process and make little alterations
along the way.



I don't think you will be able to add much in the rainbow colors to
specimens of bornite you may have. I get the impression that this material
oxidizes naturally to colorful material naturally and quickly. If the
chalcopyrite is already oxidized you may or may not be able to make it
iridescent. It is has a black crust there if probably not all that much that
you could do that would make sense. If it is lightly coated you may be able
to remove the coating with ironout or acid and then treat it to make it
iridescent.

Rock