What is an example of a hard material mentioned?

Diamond is an excellent example of a hard material. Hardness in materials is often measured by their ability to resist scratching or indentation. Diamonds are well-known for their exceptional hardness, ranking at the top of the Mohs scale, which is a scale used to rate the scratch resistance of various minerals. This remarkable property is why diamonds are often used in cutting tools and abrasives, as well as in jewelry, where durability is valued.

In contrast, the other materials listed—gold, wood, and plastic—do not exhibit the same level of hardness as diamonds. Gold is a soft metal that can be easily deformed; wood can be scratched or dented more easily; and plastic, depending on its type, can also remain relatively soft, making it less resistant to wear and tear compared to diamond. Thus, diamond stands out distinctly as a quintessential hard material.