A porous,lightweight,siliceous sedimentary rock composed of the shells of diatoms or radiolarians or of finely weathered chert,used as an abrasive and a polish.

• 硅土，一种包含有硅藻土或砂藻土或已风化石粉末的黑硅土的脆而轻的硅沉积岩，用作研磨剂和抛光剂。