Blackboard ‘chalk’ are produced especially for use with blackboards in white and also in various colours. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk rock or limestone, while colored or pastel chalks are made from calcium sulfate in its dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite). As compared to whiteboards, blackboards still have a variety of advantages: On the other hand, chalk produces dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and according
Blackboard bold written as codice_2. The codice_3 package loads codice_1. In Unicode, a few of the more common blackboard bold characters (C, H, N, P, Q, R and Z) are encoded in the Basic Multilingual Plane (BMP) in the "Letterlike Symbols (2100–214F)" area, named DOUBLE-STRUCK CAPITAL C etc. The rest, however, are encoded outside the BMP, from codice_5 to codice_6 (uppercase, excluding those encoded in the BMP), codice_7 to codice_8 (lowercase) and codice_9 to codice_10 (digits). Being outside the BMP, these are relatively new and not widely supported. The following table shows all available Unicode blackboard bold characters. The symbols are nearly