The coefficient of friction (COF) of Filled Irelands Donegal Grey Quartzite tiles can vary depending on various factors such as the surface finish, texture, and the presence of any additional coatings or treatments. It is best to consult with the manufacturer or supplier of the tiles to obtain the specific COF value for the particular product in question. They should be able to provide you with the necessary information to ensure that the tiles meet your specific needs and requirements.