Which mineral property describes how a mineral breaks along smooth planes?

• A. Fracture
• B. Luster
• C. Hardness
• D. Cleavage

Answer: (D)

Cleavage describes how a mineral tends to break along flat, smooth surfaces that follow planes of weakness in its crystal structure. This happens because the bonds are weaker in those directions, so when the mineral is stressed, it splits along those planes rather than breaking irregularly. That’s why it’s described as breaking along smooth planes. Fracture, by contrast, is when a mineral breaks with rough, uneven surfaces. Luster is about how light reflects off a mineral’s surface, and hardness is about how resistant it is to scratching. An example to picture cleavage: mica you can peel into thin, flat sheets.