The term ‘hard stone’ is often incorrectly used to refer to semi-precious stones, distinguishing them from more precious stones like sapphires, rubies, diamonds, etc. All gemstones are classified by different indexes, including a hardness index, which indicates their resistance to scratching and chipping. Gemstones used in jewelry usually have a high hardness index, but as hard as a gemstone might be, it is still delicate when set in jewelry.