A pseudomorph is a mineral that has taken on the external shape of another mineral while retaining its own internal structure. This process occurs when one mineral replaces another through chemical reactions, often leaving the original form intact. For example, a quartz crystal can form a pseudomorph of calcite if the calcite dissolves and is replaced by quartz. Pseudomorphs can provide valuable information about geological processes and the conditions under which minerals formed. They are often studied in the field of mineralogy and can be found in various locations around the world. Collectors and enthusiasts appreciate pseudomorphs for their unique appearances and the stories they tell about Earth's history.