Cleavage is defined by which two features?

• A. The angle between adjoining cleavage planes
• B. The color of the mineral
• C. The hardness of the mineral
• D. The luster of the mineral

Answer: (A)

Cleavage describes how minerals break along flat, parallel surfaces that form along planes of weakness in the crystal structure. The key feature that defines how this break occurs is the orientation of those planes, specifically the angle between adjoining cleavage planes. That angle tells you how the planes meet and therefore how the mineral will fracture along those smooth surfaces. The other properties listed—color, hardness, and luster—describe different aspects of a mineral and do not determine how it cleaves.