The exchange office can be accessed via the global buildings section in the player profile. In this building, gemstones can be traded in for one another. In addition a random gemstone can be received as a free gift every view hours.

Claiming the gemstone gift triggers a random gemstone drop.
The stone will be added to the respective gemstone storage. After activation you will have to wait a certain amount of time to trigger the next gemstone drop. This cool-down can be reduced by upgrading the exchange office.

The „exchange gems“ function allows you to trade in gems for one another. Every kind gem has a certain value that dictates how many gems of a different kind have to be paid to receive one gem of the respective kind. Only a certain kind of gem can be traded for a certain other kind of gem:

Exchange rates can be reduced by upgrading the exchange office.