Ceramic milling media
From PyroGuide
Ceramic milling media is a variety of non-sparking milling media made of aluminium oxide, used for milling chemicals which are likely to be ignited by sparking media (black powder), or chemicals which are likely to react with conventional metal media (acids). While it is not as heavy, and therefore not as effective as lead or stainlees steel media, it is still widely used in ball mills for many chemicals and compositions.