This superior chalk is 95% pure calcium carbonate and free of foreign materials that work their way into the board surface causing scratching, streaking and pitting. Chalk makes clean, smooth lines and erases easily. Best if used on natural slate and similar surfaces. Details: White 3.75" x 0.375" piece size 144 packs (12 pieces per pack, 1,728 total pieces) 95% pure calcium carbonate Free of foreign materials AP certified nontoxic For ages 5 and up