The Free Spins feature is triggered when three or more Mermaid Coins appear in the reel. During the Free Spins, the selected Gem for the Free Spins acts as below:
Ruby: During each spin, a random number of Rubies are thrown out of the Volcano, which acts as Wild.
Opal: All wild Opals apply a multiplier to any win they participate in. If there is more than one Wild in a win, the total is multiplicative.
Sapphire: If a Sapphire Volcano lands in place, it expands to fill the reel.
Jade: Any Wild Jade Volcanolanding in the reel stays stay in place for the duration of Free Spins.