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 color3.75" x 0.375"12 pieces per boxSet of 36 boxes432 pieces total95% pure calcium carbonateFree of foreign materialsAP Certified non-toxic