It is not possible to provide an accurate response to your question as the coefficient of friction can vary depending on factors such as the specific manufacturing process, any surface treatments applied, and the specific conditions in which the tiles are used. The coefficient of friction is usually determined through testing conducted by the manufacturer or a third-party laboratory. Therefore, it is recommended to reach out to the manufacturer of Acid Washed Finish Switzerlands Verde Andeer Gneiss tiles for the specific coefficient of friction information for their product.