1,non-toxic;no dust. 2,natural mineral without any chemical ingredients. 3,1pc slate pen equals 20pcs common chalk for using. Basic Information: Item No.ColorQty/CtnG.W.(KGS)N.W.(KGS)Ctn Size(CM)OB-50white2400191739*39*28Features1,slate pen,the same function as traditional chalk.2,which is made of natural mineral without any chemical ingredients;no dust, environment protection.3,size:80*6.4mm.4, ...