Which of the following is NOT a property of diamond?

The property of diamond that sets it apart is its structure, which consists of carbon atoms bonded in a three-dimensional lattice. This arrangement gives diamond its very high melting point and incredible hardness, making it one of the hardest natural substances known.

Diamonds do not conduct electricity effectively, which is primarily due to the lack of free-moving electrons. Unlike metals, which have delocalized electrons that enable electrical conductivity, the electrons in diamond are held tightly in place due to strong covalent bonds. This lack of free-moving charge carriers is why diamond is considered an insulator.

Therefore, the correct identification of the property that is not characteristic of diamond is related to its conductivity.