These are Campo del Cielo Nickel-Iron Crystals Meteorites from Campo del Cielo, Argentina, and are around 4-6,000 years old. Prepared by super-cooling and fracturing.
The first record of the Campo del Cielo meteorite was in 1576. A Spanish governor learned of the iron from the Indians, who reportedly believed that it had fallen from heaven. The governor sent an expedition under Captain de Miraval, who brought back a few pieces of a huge iron mass he called Meson de Fierro (large table of iron). The location of the find was the Campo del Cielo (field of the sky or heaven), a fitting name for the location of a meteorite. Since the Indians believed that the irons fell from heaven, the name may have come from the meteorites. The area is an open brush-covered plain that has little water and no other rocks- good country in which to find meteorites.
The crystal fragments are obtained by super-cooling a large meteorite in liquid nitrogen and striking it with a hammer. Your specimen is stable and treated with light gun oil. It should require minimum maintenance, other than an occasional brush should any signs of rust appear.