It's a 100% way to level up your gem. To super merge, you will need five gems of the same level.
You can merge any type of gem, but they have to be of the same level. The final gem type is chosen randomly if there are different types of gems in the merge.
The cost of a single merge attempt depends on the level of all gems and the amount of gem stats (one — Alexandrite, Sapphire, Ruby, Limonite; two — Diamond). The cost per merge depends on KCAL's current market price. That way, we can ensure a stable price in fiat equivalent and provide additional support for the game economy.