Black Opal

Black Opal is a special gem created by combining Perfect Opal, Flawless Diamond and Normal Aquamarine.

It is a single-target gem which can be upgraded once to Mystic Black Opal for 250 gold. The upgraded mode will boost the damage of all towers within 171 range by 40%. This will effect the towers already in place when the Black Opal is upgraded to Mystic Black Opal; towers built within the range after the upgrade to Mystic Black Opal is made will not get any damage boost. Note that the damage boost range of 171 of Mystic Black Opal is larger than the actual fire range which is only 143.

This doesn't conflict with Yellow Sapphire, as that will never override black opal's damage boost and black opal will always override its when applied.