Jovi Box of 10 Dustless Chalks for Blackboard. Compact chalk with no dust deposit, made of high quality natural raw materials (98% calcium carbonate). These chalks for blackboards/ slate are odourless, solvent-free and non-greasy, making it easy to write, providing clear and legible lines. In addition, Jovi chalks are very easy to dry erase and very durable, with a breaking point of 5.5 kg. Ideal for all sorts of boards and slates they will not scratch their surface.