pseudomorph

thumb|Pseudomorph of goethite after [[pyrite ]] thumb|Silica pseudomorph after [[gypsum crystals and silicified serpulid polychaete tubes]]

In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another due to alteration, or chemical substitution, dissolution and refilling, structural changes or incrustation. The name literally means "false form". Terminology for pseudomorphs is "replacer after original", as in brookite after rutile. The term pseudomorphoses was initially used by Haüy.