Pseudomorphism

Pseudomorphism is a process where one mineral's crystal form is replaced by another mineral's crystals, but the overall shape remains the same. Imagine a sponge that keeps its shape but is filled with a different material; similarly, in pseudomorphism, the original mineral’s external form is preserved while the internal material changes. This occurs naturally through mineral alteration or replacement, often over long periods, resulting in a new mineral that visually resembles the original but has a different composition.