Editing Pseudomorph (section)

==Substitution pseudomorph==
[[File:Native copper pseudomorph after aragonite, western Bolivia.jpg|thumb|Native copper pseudomorph after [[aragonite]], with red [[cuprite]] and green [[malachite]] alteration]]

A '''substitution pseudomorph''' is a pseudomorph in which one mineral or other material is replaced by another. The original shape of the mineral remains unchanged, but chemical composition, color, [[hardness]], and other properties change to those of the replacing mineral.  

This happens typically when a mineral of one composition changes by [[chemical reaction]] to another of similar composition, retaining the original crystalline shape. It can occur due to the loss of water or through the action of atmospheric agents, such as oxidation, hydration, or carbonation. An example is a change from [[galena]] (lead sulfide) to [[anglesite]] (lead sulfate) by oxidation. Pyrite crystals transformed into [[limonite]], a compact mixture of iron oxides where [[goethite]] generally predominates, are common. In some cases, only partial replacement occurs. The resulting pseudomorph may contain an unaltered core of galena surrounded by anglesite that has the cubic crystal shape of galena.