pseudomorph
noun
pseu·do·morph ˈsü-də-ˌmȯrf 
1
: a mineral having the characteristic outward form of another species
2
: a deceptive or irregular form
pseudomorphic
ˌsü-də-ˈmȯr-fik
adjective pseudomorphism
ˌsü-də-ˈmȯr-ˌfi-zəm
noun pseudomorphous
ˌsü-də-ˈmȯr-fəs
adjective 
Word History
Etymology
probably from French pseudomorphe, from pseud- + -morphe -morph
First Known Use
1839, in the meaning defined at sense 1