A culet is the bottommost point on a faceted gemstone.
    ______ ,----the table (upper line)
   /______\ ,----the girdle (lower line)
   \      / 
    \    / <----the pavilion
     \  /   
      \/ <----the culet
Technically, the culet only exists if a facet is cut there. In other words, a cabochon never has a culet, nor does a faceted stone with a sharp point where the culet should be. A facet on the culet is desirable because 1) a facet will assist in light dispersion and scintillation and 2) a pointed culet is more prone to chips and breaks.

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