Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
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