The Collaborative International Dictionary of English v.0.48:

Gummite \Gum"mite\, n. [So called because it occurs in rounded
   or flattened pieces which look like gum.] (Min.)
   A yellow amorphous mineral, essentially a hydrated oxide of
   uranium derived from the alteration of uraninite.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gummite
    n 1: a gummy orange mixture of uranium oxides and silicates
         occurring naturally in the hydration and oxidation of
         pitchblende