Gem

Gems are small objects that grant bonuses when socketed into items. There are four types of gems in Diablo III; Amethysts, Emeralds, Rubies and Topazes, which are found in 15 levels of quality. (The 15th, Marquise, was added in Patch 1.0.7.) Only the first eight levels can be found from monsters or chests, with Flawless Squares the highest quality (and the only type that drops in Inferno). Higher levels of gems can only be crafted (for a price) by the Jeweler, and the costs grow and accumulate impressively.

Creating a level 14 gem is quite a chore. The total costs, assuming a starting point in Inferno where Flawless Squares drop, is 729 Flawless Squares, 15,400,000 gold and 1631 Tomes of Secret, for each Radiant Star gem.

As of patch v1.07, there is no way to create or add sockets to items. During development the Jeweler was set to add sockets to items, but this ability was shelved pre-release, leaving players able only to hope for socket finds. It's often hoped that socketing might come back as a quest reward or for a price, in a patch or more likely in D3X.

Diamonds are confirmed as being introduced in Reaper of Souls.

Gems are a very useful item to twink to new characters, as gems have no level requirements. Items with sockets are first found around level 15 (some legendary items have sockets as low as level 10), in late Act One or early Act Two, and it's quite easy to add a gem with a bonus much larger than that of the item itself. Low level weapons with a high level Ruby in them become wildly overpowered, but that's the whole fun of it for many players.

See the Diablo 2 Gems page for details on that game's seven types of gems (skulls, diamonds, and sapphires do not appear in Diablo 3).

Diablo III Gems

Gems in Diablo 3 have evolved during the game's development. Though the concept of 14 levels of quality has remained constant, the types of gems, their names and graphics, and the materials and costs to upgrade them have evolved repeatedly.

See the Gems archive info for full details on their development.

Weapons

A socket in a weapon is considered almost essential, at the end game. Rubies were always popular at low or mid levels, and they became much more useful in Patch 1.0.7 when their values in weapons were considerably upgraded. That said, Emeralds are the weapon socket of choice for most high levels characters, especially those with a healthy Critical hit Chance value. Amethysts are a not unheard of for Hardcore players, for their life on hit.

Diamonds will come with Reaper of Souls and will boost elite damage in weapons.

Helms

Sockets in helms are even more desired than in weapons, to the point that virtually no end game helm is considered viable without a socket.

Rubies are the most popular for the +%experience per kill. This bonus was irrelevant in the end game until the debut of the Paragon system, at which point it became the most sought after.
Amethysts are popular, especially for Hardcore characters, since the +%life bonus is a huge source of hit points, leveraging already high vitality bonuses.
Topaz are also sought for the Magic Find bonus, while gold farmers may enjoy Emeralds for that bonus.
- The Topaz vs. Ruby debate is an interesting one, since high level players mostly seek paragon levels for the 3% bonus to Magic Find and Gold Find per level. Yet an affordable Star topaz grants 25% Magic Find, which is equivalent to the MF gain of more than 8 Paragon levels.
Diamonds will come with Reaper of Souls and will reduce cooldown.

Other

All other items are given the "other" designation. Sockets are found in rare and magical pants, chest armor, off-hand items (such as quivers, mojos, orbs, shields, etc) amulets, and rings, but not in shoulders, bracers, belts, or boots. (A few legendary and set items add sockets to other pieces of armor, such as the socket in Ice Climbers boots or Tasker and Theo gloves.)

Softcore players almost always go for +damage via a boost to their mainstat.

Emeralds for dexterity for Demon Hunters and Monks.
Rubies for strength for Barbarians.
Topaz for intelligence for Wizards and Witch Doctors.
Diamonds will come with Reaper of Souls and will apply a resist all bonus to armor.

Hardcore characters are much more likely to use Amethysts to boost their vitality.

Upgrading Gems

Gems can be upgraded by the Jeweler, for a price. First of all, the Jeweler needs to be trained to his maximum level in order to craft the highest level gems. Even then, he can only upgrade gems to the 11th quality level, and just be taught the 4 highest tiers in each gem type by Designs that drop from monsters or objects. Jeweler Designs and Blacksmith Plans dropped very rarely until Patch 1.0.7 buffed their drop rates 4x.

All plans and designs can also be purchased from the Auction House, where their prices have steadily dropped over time. (Whe new recipes are introduced in patches, such as the level 63 items and Marquise gems in Patch v1.0.7, their values were very high for a day or two, before falling rapidly.)

All gem upgrades cost gold, and most require some materials as well. Lower level recipes are quite cheap in terms of gold and materials, and only require 2 gems to upgrade to the next level. Higher level gems require a lot of gold and materials, and it takes 3 gems to make 1 of the next rank. At the 2 > 1 upgrade ratio introduced in v1.03 (prior to that all upgrades were 3 > 1, plus much higher gold prices), it would require 256 chipped gems and 570 gold to create 1 Flawless Square (which is the highest gem that drops), though no one actually collects that many chipped gems since higher quality gems can easily be found.

When considering upgrade prices, bear in mind the cumulative costs, which are listed in the last column of the table below. For example, the price to make the 14th level gem, a Radiant Star, is 400k gold + 20 Tomes of Secret + 3 Flawless Stars. That doesn't sound so bad, until you realize that each of those Flawless Stars had to be made from requires 3 Perfect Stars, and 9 Flawless Stars, and 27 Stars, and so on, down to the Flawless Squares that form the base of the gem economy.

It requires a total of 729 Flawless Squares, 1631 Tomes of Secret, and 15,400,000 gold to make a single Radiant Star, not counting the gold required to upgrade the Jeweler in the first place, or to obtain the three highest level plans for each gem. Even assuming you had all the Flawless Squares, Tomes of Secret, and over 15 million gold in your stash, creating a Radiant Star would still take you 243 clicks on the Jeweler's upgrade bar. At 3 seconds per click, that's 729 seconds, or close to 12 minutes doing nothing but clicking the "Upgrade" bar in the Jeweler's interface.

And the Marquise Gems introduced in Patch 1.0.7 require 3 Radiant Stars each.

Gem Result	Gold Cost	Gems Required	Materials	Cumulative Cost [e]
Chipped	N/A	N/A	N/A	Find them.
1 Flawed	10 gold	2 Chipped	None	Find them.
1 Regular	25 gold	2 Flawed	None	Find them.
1 Flawless	40 gold	2 Regular	None	Find them.
1 Perfect	55 gold	2 Flawless	1 page of Jewelcrafting	Find them.
1 Radiant	70 gold	2 Perfects	1 Page of Jewelcrafting	Find them.
1 Square	85 gold	2 Radiant	1 Tome of Jewelcrafting	Find them.
1 Flawless Square	100 gold	2 Squares	1 Tome of Jewelcrafting	Find them.
1 Perfect Square	30,000 gold	3 Flawless Squares	3 Tomes of Secret	30k gold & 3 ToS (3 Flawless Squares)
1 Radiant Square	50,000 gold	3 Perfect Squares	6 Tomes of Secret	+ 30k gold & 3 ToS + 30k gold & 3 ToS + 30k gold & 3 ToS + 50k gold & 6 ToS = 140k gold & 15 ToS (9 Flawless Squares)
1 Star	80,000 gold	3 Radiant Squares	9 Tomes of Secret	140k gold & 15 ToS + 140k gold & 15 ToS + 140k gold & 15 ToS + 80k gold & 9 ToS = 500k gold & 54 ToS (27 Flawless Squares)
1 Flawless Star	100,000 gold	3 Stars	12 Tomes of Secret	500k gold & 54 ToS + 500k gold & 54 ToS + 500k gold & 54 ToS + 100k gold & 12 ToS = 1600k gold & 174 ToS (81 Flawless Squares)
1 Perfect Star	200,000 gold	3 Flawless Stars	15 Tomes of Secret	1600k gold & 174 ToS + 1600k gold & 174 ToS + 1600k gold & 174 ToS + 200k gold & 15 ToS = 5000k gold & 537 ToS (243 Flawless Squares)
1 Radiant Star	400,000 gold	3 perfect stars,	20 Tomes of Secret	5000k gold & 537 ToS + 5000k gold & 537 ToS + 5000k gold & 537 ToS + 400k gold & 20 ToS = 15400k gold & 1631 ToS (729 Flawless Squares)
1 Marquise Gem	20,000,000 gold	3 Radiant Star Gems	10 Demonic Essence	66.2 million gold + 4893 Tomes of Secret + 2187 Flawless Square Gems + 10 Demonic Essence

Full List of Gem Properties

All gems and their bonuses, with game data pulled directly via the Database database.

Marquise Gems

Marquise Gems were added in Patch 1.0.7 as the new, highest level gem. They are meant to serve as something of a gold sink, with a considerably higher creation cost than earlier levels of gems, despite adding only marginally to the function.

Marquise Emerald

Weapon: Increased Critical Hit Damage by 110%
Helm: +33% Extra Gold from Monsters
Armor: +62 Dexterity

Marquise Topaz

Weapon: Melee attackers take 2500 per hit
Helm: 33% Better chance of finding magical items
Armor: +62 Intelligence

Marquise Amethyst

Weapon: Each Hit adds +700 Life
Helm: +19% Life
Armor: +62 Vitality

Marquise Ruby

Weapon: +160 Minimum and +160 Maximum Damage
Helm: Increases Bonus Experience by 33%
Armor: +62 Strength

Rubies Buffed

Patch 1.0.7 introduced Marquise Gems and also reworked Rubies, greatly increasing their damage when socketed in weapons. This was intended to make them a viable alternative to Emeralds, which were virtually the only gem socketed in weapons (at least in Softcore. In Hardcore Amethysts enjoyed some popularity for their Life on Hit bonus.)

From the official patch notes:[1]

All ruby gems have had their weapon bonuses increased (these changes will apply to both existing rubies, as well as new rubies):

Chipped Ruby: +3 minimum damage/+3 maximum damage (up from +2/+2)
Flawed Ruby: +6 minimum damage/+6 maximum damage (up from +4/+4)
Ruby: +9 minimum damage/+9 maximum damage (up from +8/+8)
Flawless Ruby: +12 minimum damage/+12 maximum damage (up from +10/+10)
Perfect Ruby: +15 minimum damage/+15 maximum damage (up from +11/+11)
Radiant Ruby: +18 minimum damage/+18 maximum damage (up from +12/+12)
Square Ruby: +21 minimum damage/+21 maximum damage (up from +13/+13)
Flawless Square Ruby: +25 minimum damage/+25 maximum damage (up from +14/+14)
Perfect Square Ruby: +30 minimum damage/+30 maximum damage (up from +15/+15)
Radiant Square Ruby: +40 minimum damage/+40 maximum damage (up from +16/+16)
Star Ruby: +60 minimum damage/+60 maximum damage (up from +17/+17)
Flawless Star Ruby: +80 minimum damage/+80 maximum damage (up from +18/+18)
Perfect Star Ruby: +100 minimum damage/+100 maximum damage (up from +19/+19)
Radiant Star Ruby: +130 minimum damage/+130 maximum damage (up from +20/+20)
Marquise Ruby: +160 minimum damage/+160 maximum damage.

These rubies have also had their bonus damage calculations changed, and will now add damage flatly to both the minimum and maximum values on weapons:

For example, if you have a weapon that does 150-200 damage and you socket a Perfect Square Ruby (which adds +30 minimum damage/+30 maximum damage), your weapon will do 180-230 damage.

Future Gem Changes

Further gem changes and modifications are expected in future patches and expansions.

For instance, the developers have discussed entirely reworking the reflects damage / thorns system, which would involve greatly buffing or reworking the bonuses granted by Topaz gems in weapons.

References

Gem

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