These are meteorite shale fragments that originate from the area around the Canyon Diablo impact crater in Arizona. The desert around the crater is littered with rusted scraps of nickel iron (meteorites) and these fragments of shale that are in various stages of oxidation. When the giant iron impactor slammed into the desert floor, the resulting catastrophic explosion vaporized a large portion of the meteorite. Many thousands of fragments of this material was scattered around the desert. Most of it is very tiny and can only be noticed after a magnet is dragged through the desert sand.
Refer to the photo. The black centimeter cube is shown for scale and is not included. You are purchasing several small fragments of shale selected from the larger lot shown. Your purchase will include a labeled gemjar for safe storage.