Here is the full list of all 12 Hexic HD achievements worth 200 gamerscore. It takes around 20-25 hours to unlock all of the achievements on Xbox 360.
150,000 Points in Marathon
25 Total Combos
Bonus-Star Cluster
Black Pearl
5000 Total Combos
Beat Survival
75,000 Points in Timed
1,000,000 Total Points
Starflower
Form a cluster of three black pearls.
Complete 100 games of Hexic.
Surround one piece with six black pearls.