Iron silicate arises as side product during the copper refining process. It’s the slag that floats on top of the molten metal. When quenched in water the slag turns into a granules which then gets further processed into iron silicate fines and iron silicate stone.
The fine grained and sharp edged iron silicate is well suited for abrasive blasting also known as sandblasting. Thereby a stream of iron silicate gets pushed against a surface under high pressure. This results in the surface getting sanded which is a common to remove surface contaminants. It’s also possible to use abrasive blasting to smoothen surfaces with less pressure.