Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
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