what does "corrupted" on normal gems mean?

sometimes when I hover my mouse over a gem in a guide in the forums, I see "Corrupted" (not Vaal gems) but it doesn't say how they are corrupted or what that means for the gem, what does it mean?

I am hovering my mouse over a gem called "Faster Attacks Support" but I don't understand what "corrupted" means.



https://imgur.com/LACtP5A

The "Corrupted" modifier means it has been touched by one of the dark sources of power in Wraeclast, which, for gameplay purposes, generally means it can no longer be modified, somewhat like Mirrored items. Probably the most noticeable gameplay impact for Corrupted skill gems is that you won't be able to use GCP on them nor use them for vendor recipes (or so I've heard - haven't actually tried that, but I wouldn't expect them to work).

(The effects of using a Vaal Orb on a skill gem can have some exciting effects other than simply adding the Corrupted modifier - it can also give +1 level, -1 level, up to +10% quality, and up to -10% quality, with the ability to reach +1 over max level if it is max level and then rolls +1 level, or reach +3% quality over max quality if it was already max quality. This is randomly determined with uneven weighting, which means it is unlikely for these beneficial outcomes to occur.)

hmmm... interesting. Thank you