The four gems in Dracca are rare crystals without any interest for dragons: they cannot use these to heal them and cannot take any strength from these. Therefore, they are used as a money because of they lightness, resistance and beauty. The rare creatures that can eat these gems usually not use these as money, and favor other ways for trading.
Topaz is the basic money for dragons and other living creatures on Dracca. It can be of several different colors, depending on the island they were extracted from. You can then have blue, pink, yellow and green Topazes in your neck pouch. That's why some sellers refuse to take Topaz from other island, and only accept the local money.
A bit more rare, a Tourmaline is worth 4 Topazes. Sellers sometimes don't have change. Tourmalines can be green (most spread one), pink or blue (rare).
Ruby is used for bigger tradings, and is rarely used for everyday life. It can be artificially made by some nations. Its value is set to 10 Tourmalines, or 40 Topazes. There are only red rubies, but artificial ones are paler than the natural ones, looking almost pink pastel.
The most valuable of all gems, Diamonds are only used for biggest deal, including illegal traffics. It cannot be made artificially, so its value is very stable and high. A Diamond is worth 2 Rubies, so 80 Topazes (or 20 Tourmalines). Transparent, they sometimes have a very slight pale color.
|Tourmaline||Green, pink or blue||4|