From Diablo Wiki
Star Gems are the 11th level of gem, and perhaps the most commonly used in armor socketing by high level characters. Stars are popular for providing excellent utility for their price. They can be created without too much difficulty from found objects (27 Flawless Squares + 51 Tomes of Secret + 500k in Jeweler fees), and give a clear benefit over lower level gems, while higher level gems cost a great deal more for relatively minor increases in performance.
For instance, a Perfect Star yields just 8 more points to a given stat when socketed in armor, yet costs roughly 10x more than a Star gem. (A Perfect Star requires 9 Stars, plus upgrade costs and materials to create.)
The main exception to this rule of thumb comes from Emeralds in weapons, where most players consider another 10% Critical hit Damage a necessity at almost any price. (Rubies in weapons became much more viable in Patch 1.0.7, and their bonuses increase more with higher level rubies, rather than just 10% more per level, as with Emeralds.)
Star gems can only be created by the Jeweler from Radiant Square gems, and are used to create Flawless Star gems.
- 3 Radiant Square gems (same type) + 100 gold + 1 tome of Jewelcrafting = 1 Flawless Square gem
To upgrade to the next level, the Perfect Square:
- 3 Flawless Square gems (same type) + 30,000 gold + 3 Tomes of Secret = 1 Perfect Square gem.
See the gems article for every gem crafting recipe and cumulative cost breakdowns.
Flawless Square Gem Stats
The stats for all types of Flawless Square Gems, as of Patch 1.0.7. (Rubies in weapons did less damage in earlier versions of the game.)
A full list of gems in ascending order:
- Flawless Square
- Perfect Square
- Radiant Square
- Flawless Star
- Perfect Star
- Radiant Star
- Marquise Gem (Added in Patch 1.0.7.)
|Items of Diablo III  Item Basics Normal Items Crafting Legendary Armor I Legendary Armor II Legendary Weapons 1h Legendary Weapons 2h Item Sets|
|Item Basics||Item Affixes||Interface||Artisans||Miscellaneous |
• Prefixes & Suffixes
|Diablo 3 and Reaper of Souls Item Sets||Reaper of Souls only |
Crafted Item Sets
Crafted Item Sets
Themed Item Sets