pseudomorph

A false, deceptive, or irregular form.

A mineral that has the crystalline form of another mineral rather than the form normally characteristic of its own composition.

A deceptive, irregular, or false form; specifically, in mineralogy, a mineral having a definite form belonging, not to the substance of which it consists, but to some other substance which has wholly or partially disappeared.

An irregular or deceptive form.

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.

A mineral that formed by replacement of an existing mineral (or organic matter) such that the new mineral has the appearance and dimensions of the original.