Pumice doesn't have a defined cleavage like many other minerals. This is because pumice is not a true mineral, but a volcanic glass.

Here's why:

* Cleavage refers to the tendency of a mineral to break along specific planes of weakness in its crystal structure.

* Pumice is formed from rapidly cooled lava that traps gas bubbles, creating a porous and lightweight material. It lacks a defined crystal structure, so it doesn't exhibit cleavage.

Instead of cleavage, pumice fractures conchoidally, meaning it breaks in smooth, curved surfaces like a shell.

Let me know if you have any other questions!