However, some other non-mineral rocks (such as lapis lazuli) or organic materials can also be also used for jewelry and are called gemstones. These include amber or jet. Pearls and coral are sometimes also called gemstones.
The Ancient Greeks began to decide which gems are precious and semi-precious. This continued in other cultures. In modern times, the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious.
Types of gemstones
Jewel Facts for Kids. Kiddle Encyclopedia.