pseudomorph

from The Collaborative International Dictionary of English v.0.48

Pseudomorph \Pseu"do*morph\, n. [See {Pseudomorphous}.]
   1. An irregular or deceptive form.
      [1913 Webster]

   2. (Crystallog.) A {pseudomorphous crystal}, such as a
      crystal consisting of quartz, but having the cubic form of
      fluor spar, the fluor crystal having been changed to
      quartz by a process of substitution.
      [1913 Webster]