Learn · Gemstones and pearls
Gem treatments explained
Most coloured gems in the trade have been treated in some way: heated, oiled, filled, irradiated. Treatment is normal; not saying so is not. Look up a gem's usual treatments and what they mean for care and for the bench, read what each trade code stands for, and check when the US rules require you to disclose it.
Pick a gem to see its usual treatments, or answer the three questions to check disclosure.
Read the guide
Hue, tone and saturation
How the trade describes a coloured stone's colour: hue, tone and saturation
Birthstones around the world
Every month on the American, British, Japanese and nine-gem lists
Where gems come from
A world map of where each gem is mined, today and historically
The 7 pearl value factors
GIA's seven pearl value factors, changed one at a time on one pearl
Cutting angles and light
Change a stone's cutting angles and follow the light: where it returns and where it leaks Preview