Gemstones, such as diamonds, rubies, sapphires, emeralds, aquamarines, and tourmalines, are minerals.

Gemstones, such as diamonds, rubies, sapphires, emeralds, aquamarines, and tourmalines, are nonmetalic minerals.
As the name itself says, these minerals do not contain any metal inside of them, but are rather valuable both because of this and because of their beauty which is highly-praised on the market. There are also many other types of minerals, but these are the most valuable ones.