Width x Depth x Thickness: 13.8 x 9.8 x 0.2 inches (350 x 250 x 5 mm); Just slate board material: Natural slate is a plate type of aquamarine stone. The natural slate is delicate, less absorbent, and has a unique pattern that is resistant to alkali and acid. It is widely used in Europe as a roofing material and is used in the Monastery of Mont Saint Michelle, the Louvre Museum of Paris. Due to the use of natural materials, there may be slight differences in size.