Diamond Dust and Diamond Berg are two of the more powerful single-target Psynergies, available only in The Lost Age and Dark Dawn. They are exclusive to Piers and Amiti when they are in their Mariner class series and Aqua Squire Class Series (only Mercury Djinn set).
An "attack with crystalline ice", Diamond Dust resembles a long group of large chunks of ice slamming into the enemy. Available to the Mariner, Privateer, and Commander classes, it is learned at lv. 16. Diamond Dust costs 6 PP to cast and strikes the target with Mercury power equal to the user's own attack power with 34 damage points added to the result.
It is available to Amiti in his Aqua Squire, Aqua Knight and Aqua Prince classes.
Described as "freez[ing] and crush[ing] a foe", Diamond Berg is the attack that replaces Diamond Dust after Piers reaches the Captain class. It appears as a massive block of ice (the namesake iceberg) crashing down upon the target. Piers then physically strikes the frozen foe repeatedly, chipping off more ice with each blow. Diamond Berg is often regarded as Pier's "ultimate" attack by players, despite the fact that its high cost puts a strain on his low Psynergy supply (compare to Odyssey). Diamond Berg costs 17 PP to use and strikes the target with Mercury power equal to the user's own attack power with 92 damage points added to the result.
This is the same for Amiti. This is available in his Aqua Lord and Aqua Master classes.