Question

What is the difference between precious and semiprecious stones?

Answer 1

The difference between precious and semiprecious stones dates back to the ancient Greeks.

Explanation:

A gem or gemstone is a piece of crystal which can be polished and made into jewelry. Some other materials like pearls are also considered gemstones.

In modern usage there are four gemstones which are considered precious stones. These are diamond, ruby, sapphire and emerald. All other gems are semiprecious stones.

The classification of gems is old. Different gems can be made of the same material but have different colour. A good example is corundum `Al_2O_3`. Impurities in the crystal give it colour. If a corundum crystal is red is is a ruby. If it is any other colour it is a sapphire.

Even more strange is the mineral beryl `Be_3Al_2(SiO_3)_6`. If it is green it is the precious stone emerald. If it is any other colour it is a semiprecious stone such as blue aquamarine.