A research stone is an item in Evony TKR (The King's Return).
The description of Research Stone in Evony TKR says:
Necessary item to research high level Technologies.
Research Stone is known to potentially be obtainable from opening Junior Lava Turtle Chest, Medium Lava Turtle Chest, Senior Lava Turtle Chest, Junior Witch Chest, Medium Witch Chest, Senior Witch Chest, Junior Warlord Chest, Medium Warlord Chest, Senior Warlord Chest, Legendary Lava Turtle Chest, Legendary Witch Chest, Legendary Warlord Chest and Epic Witch Chest. The links for each item are below:
Note: This list may be incomplete.