What unique property of diamonds is utilized in their separation from ore?

The unique property of diamonds that is utilized in their separation from ore is their attraction to grease. This method exploits the fact that diamonds have a natural affinity for certain types of grease, allowing them to adhere to it while other materials do not. This property is pivotal in the separation process during diamond mining; when combined with a process called grease table separation, it effectively differentiates diamonds from other minerals and materials present in the ore.

The other options do not accurately reflect the properties of diamonds relevant to their separation. Diamonds are not magnetic, meaning they do not respond to magnetic fields, which rules out that method for separation. While diamonds are denser than many other materials, they do not float on water; thus, flotation is ineffective. Lastly, diamonds do not change color in heat in a way that would aid in their separation from ore, making that option irrelevant in this context.