Generally, the most useful gems are PDEF, MDEF, and PATK or MATK (depending on your class). Gems of HP, Crit, Block, or Charisma are also available. These last four gems types should be secondary to the first set of listed gems in priority.
Gems can be converted into other types of gems of the same level using the Convert tab in the blacksmith. The level of the gem to be converted determines the price in gold charged to change a gem from one type to another. Some feel it is better to level a gem as high as possible before converting it, because it is cheaper to convert one gem than the three or four gems that can be synthesized into it.
Gems come in levels of one through ten with ten offering the best stat improvement. You can improve your gems through Synthesizing. To synthesize gems of levels one through seven, you need four gems of the same type and level to create one gem of the same type and the next higher level. For example, four level one PATK gems synthesize into one level two PATK gem. For levels eight through ten, you need only three of the same type and next lower level for synthesis.
Initially, you can only improve your gems to level three. Levels four and five drop in the form of scrolls as rewards from quests and certain multiplayer dungeons. Level five PATK/MATK come from completing The Graveyard, level 5 PDEF - completing The Bloodlands, level five HP and MDEF from completing The Void.
To improve the bonuses of all socketed gems, you can use Soul Engraving.
Gem Transposer Scroll Costs
1195 Balens or Randomly drops when completing Necropolis Level 10
|Randomly drops when completing Necropolis Level 15|
|Randomly drops when completing Necropolis Level 20|
|Randomly drops when completing Necropolis Level 30|
Gem Conversion Costs
|Level 1||Level 7|
|Level 2||Level 8|
|Level 3||Level 9|
|Level 4||Level 10|
|Level 5||Level 11|
|Level 6||Level 12|
Gems can be found as rewards from