Hillman Hall of Minerals and Gems

Pseudomorphs

A mineral that has taken the crystal shape of another mineral is said to be a pseudomorph, meaning "false form."   This phenomenon can occur in various ways.

The process of pseudomorphism may be mechanical, structural, or chemical in nature and results from changes in the physical and chemical environment during or after the period of initial crystallization.  A pseudomorph is classified both by the nature of the processes by which it was formed and by the changes it experienced during those processes.

The pseudomorphic change is expressed, for example, as "aragonite (original mineral) > calcite (later mineral)."  Another way of writing it is "calcite after aragonite."

The pseudomorphs exhibit in Hillman Hall shows examples of eight types of pseudomorphism, four of which are shown below. Click on photos for larger views in a new window. Photos: Debra L. Wilson

Quartz after Calcite
Quartz after Calcite
New Mexico

Prehnite after Laumontite
Prehnite after Laumontite
India

   

Calcite after Aragonite
Calcite after Aragonite
Italy

Calcite after Ikaite
Calcite after Ikaite
Russia

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