Here is the full list of all 16 Gasnator achievements.
Find crystal at level 1
Find crystal at level 2
Find crystal at level 3
Find crystal at level 4
Find crystal at level 5
Find crystal at level 6
Find crystal at level 7
Find crystal at level 8
Find crystal at level 9
Find crystal at level 10
Find crystal at level 11
Find crystal at level 12
Find crystal at level 13
Find crystal at level 14
Find crystal at level 15
Find crystal at level 16