A pencil is an implement for writing or drawing. It is a thin core of graphite well mixed with clay, inside a wooden body as protective casing that prevents the core from being broken.
There are two types of water hardness: temporary and permanent hardness. Temporary hardness is due to the presence of calcium hydrogen carbonate Ca(HCO3)2(aq) and magnesium hydrogen carbonate Mg(HCO3)2(aq).