A Diamond Tile (or also referred to as RC Tile and white rock) is often found deep around normal Tiles, they can be found in every map, excluding Freeports. (Finch I, Finch II, (at 1/3 of the rate of Sparrow) Sparrow, Canary, and The Pits) .
In the three "normal" maps, the diamonds are placed randomly and rarely amongst normal Tiles. They must be destroyed with, and occasionally "tunnelled" into, using Ammo, although Breaker Ammo will destroy them in one hit. After destroying a Diamond Tile, it will randomly drop one RC Turret, Auto Turret or Burst Turret. However, you do not have to destroy the entire tile for this to happen, as a few hits from regular ammo will destroy the diamond before the rest of the shell.
In Canary, they are found in abundance in the centre square.