Which skill gems stack effects?

Is there an overview over which gems can stack with which other gem or themselves?

I know I can look at the tooltip of the skill to find out, e.g. that 2x added lightning damage linked to a spell does indeed add 2x the additional lighning damage, but e.g. 2x minefield support on the other hand does only add the +2 mines from a single minefield support.

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Exilyth wrote:

Is there an overview over which gems can stack with which other gem or themselves?

I know I can look at the tooltip of the skill to find out, e.g. that 2x added lightning damage linked to a spell does indeed add 2x the additional lighning damage, but e.g. 2x minefield support on the other hand does only add the +2 mines from a single minefield support.

None. You cannot gain double effect from using two of the same support gem linked to a skill. It does not work this way. Ie. If you link Spark-Added Lightning Damage Support-Added Lightning Damage Support you will only get the benefit of the higher level of the two support gems. They do not stack.

And what about other gems/gem combinations? E.g. certain skills can't be used with trap/mine support or spell totems.

Is there any place where that information can be found in one place without requiring you to scavenge through the gem feedback section for tidbits of moderator/dev comments on the special cases?

There are some interactions, like the damage mechanics of lightning ball and support skills, which are not obvious and which can also not be derived from the skill gem tooltips.

Yes, there is such a place, and it is called PoE wiki.