I have learned that these Extruded Underfoot Diamonds cut much like the gems, Taaffeite, Harmonagate, Staurolite, and Prestidigitase. The stats any of these cut gems deliver is based on two things; your level and the metal of the setting you use.
Kayrsoc is correct that the stats for a level 85 character using Temporite as the metal will produce those stats. I suspect that if you use Cosgrite, the new metal from Underfoot, you'll get higher stats. I don't currently own UF so I can't test that theory.
I have also learned that the gems will evolve with the character as they level and upgrade the metal settings. The same gem in a Dwerium setting for a level 69 character produces 24 AC 482 HP/MANA/END and 24 to all other stats and resistances. The metal settings are recyclable, but the gems are attunable and become no trade once inserted in a setting.
If you are using a setting that has slots for side gems like a duo or trio setting, the possibilities are very diverse. The side gems can focus on all of the stats including HP if a Round Cut Opal is used or MANA/END if you add a Round Cut Emerald. There are gems for all of the stats that you can utilize in the side slots of a trio or duo setting. The only restriction I have found is you cannot use two of the same gem in the same setting. These side gems derive their stats on the same basis as the main gem; your level and the metal setting used.
What is also interesting is the type of cut on your main gem can make a difference in the stats like STR, STA, CHA, AGI, WIS, INT, and DEX and you should get the cut that provides the most benefit for the character you are planning to have wear the item.
Hope this helps.
If you can post this to all similar gem posts I think it would help people to understand how these gems work and how versatile they really are.
Aadar GM Jeweler
85th Season Wizard
Antonius Bayle