* Internal arrangement of atoms (Crystal Structure): Galena has a cubic crystal structure. This means its atoms are arranged in a very specific, repeating pattern. This pattern creates planes of weakness along which the mineral easily cleaves (breaks).

* Density: Density is a measure of mass per unit volume. While density is a property of galena, it doesn't directly cause it to break into tiny pieces.

* Hardness: Hardness is a measure of a mineral's resistance to scratching. While galena is relatively soft, hardness doesn't directly influence how it breaks.

* Luster: Luster refers to the way light reflects off a mineral's surface. It's a visual characteristic and doesn't affect the mineral's cleavage.

In summary: The way galena breaks (cleavage) is determined by the internal arrangement of its atoms, which creates planes of weakness within the crystal structure.