Crayola manufactures two types of chalk, extruded and molded. Extruded chalk, such as Crayola Anti-Dust White Chalk, primarily contains calcium carbonate. Molded chalk, such as Crayola Children's Chalk (available in white or colored), is a softer chalk, made of plaster of paris. This type of chalk is not dustless and not recommended for chalkboard use.
Crayola Sidewalk Chalk is a molded chalk that is not intended for use on chalkboard surfaces. It does not include calcium carbonate. This product contains plaster of paris which has a gritty texture and may scratch your chalkboard.