The Collaborative International Dictionary of English v.0.48:

Ponderosity \Pon`der*os"i*ty\, n.; pl. Ponderosities. [OF.
   ponderosit['e].]
   The quality or state of being ponderous; weight; gravity;
   heaviness, ponderousness; as, the ponderosity of gold. --Ray.
   [1913 Webster]