Casting a spell from a spell gem doesn't require components, so generally speaking, no, you wouldn't be able to counter it. If you were somehow aware of the casting despite the lack of components, then maybe. Like, if you were concentrating on detect thoughts and had used your action on your last turn to probe the creature casting from the spell gem, I would probably rule that knowing "what is most on its mind in that moment" would make you aware that it's casting a spell, but nothing requires a DM to rule that way.
Can you counter spell form spell gem ? if Sorc use subtle spell to cast a spell and store it in spell gem it can counter or not
Casting a spell from a spell gem doesn't require components, so generally speaking, no, you wouldn't be able to counter it. If you were somehow aware of the casting despite the lack of components, then maybe. Like, if you were concentrating on detect thoughts and had used your action on your last turn to probe the creature casting from the spell gem, I would probably rule that knowing "what is most on its mind in that moment" would make you aware that it's casting a spell, but nothing requires a DM to rule that way.
Thanks! Now i can find the way to completely win the spell casting war with an item now!