Gemming for Mastery over intellect?

[fluffhead4020]

How come I see an abundance of warlocks gemming Fractured Sun's (320 Mastery) over a Brilliant Primordial(160 int)? With intellect being our primary stat, it seems strange. Also, there isn't any mastery thresholds to be shooting for where this would be necessary. Any insight?

-or an Artful over Brilliant Primordial.

[Bluesftw]

2 mastery is worth more than 1 int , been like that for a long time now , and since gems give twice as much of secondary stats than primary, noone gems int ^^

[Huntingbear_grimbatol]

Stat weights decides what you gem.
I don't play a warlock but for Ret paladins (example) Strength, our primary stat, has a stat weight of 3.34 which means 160 str gem = 160 x 3.34 = 534.4 points of value.
On the other hand secondary stat gems have 2 times the amount of rating on them (320) and because haste has the stat weight of 1.89 it means 1 gem of haste = 320 x 1.89 = 604.8

I imagine it's the same for warlocks and other classes with some gems, this doesn't take into consideration haste break points or anything like that but once you have your "caps" you should in general go for the gems or reforges etc that give you the most value.

You can check your own class and spec stat weights here if you want. http://www.maxdps.com/warlock/
Not sure if it's up to date though.

[Ichifails]

How come I see an abundance of warlocks gemming Fractured Sun's (320 Mastery) over a Brilliant Primordial(160 int)? With intellect being our primary stat, it seems strange. Also, there isn't any mastery thresholds to be shooting for where this would be necessary. Any insight?

-or an Artful over Brilliant Primordial.

Secondary stat gems have twice the amount and 320 secondary is better than 160 primary.

It's the same reason why you should gem expertise because you have 2 options:
Let's say you need 480 hit.

Now you can go about this like this:
Reforge 480 STAT into hit and have 80int + 160 STAT gems. So you would lose 480 STAT for 240 int.
Or you can not reforge the STAT and gem 160 expertise + 160 STAT. So you lose 240 int for 480 hit and you keep your STAT.