Unless I'm mistaken, if you're doing the task/quest where it asks you to loot this item, you must personally loot the item off a freshly killed mob for it to count. If you try to charm a mob and give it the large darkhollow geode, then kill it, I don't think that this will work, but I could be mistaken. Maybe charm a mob, give it this item, blur it, then try to kill it, but too much effort IMO. May be worth a shot if someone is selling the drop in bazaar at a low price though, to save the time in trying to farm the drop yourself.
*Edit. Tried the charm method tonight by charming a pet, zoning, and then logging and zoning back in to kill the mob. Didn't work. Don't waste your money on the bazaar sold item. You must personally be the one to loot this item off a mob that has this item, not a mob that had the item given to it from charming.
Found a quest from Artisan Vidi Cogsworthy in Ak'Anon while playing as my gnome. That requires you to loot one of these the name of the quest is "Darkhollow Geode".
I got this from my cultural quest NPC and found out you have to personally loot this item to count. You can't have a player give it to you after they've looted. Got one from a spider in a hive instance.