Final answer:
The property of a mineral that allows it to cleave into thin sheets is known as cleavage. It happens when minerals break along their weakest chemical bonds, producing flat, shiny planes.
Step-by-step explanation:
If a mineral cleaves into thin sheets, the property it has is called cleavage. Cleavage refers to minerals breaking along planes where chemical bonds are weakest, resulting in flat, shiny surfaces that reflect light well. This is different from luster, which is how light interacts with a mineral's surface; hardness, which is a mineral's ability to resist scratching; and streak, which is the color of a mineral's powder form when scratched against a ceramic plate.