WEEPING CRAG (FORGE LANDS)
1) The stone is hidden in the cave that you can reach through the underwater tunnel (after defeating the Stalker) and where you fight a mini-boss battle with Gorewood. More details on how to get there can be found in the Additional Locations chapter, under the Weeping Crag section.
CHARRED PASS (FORGE LANDS)
1) The stone is hidden in a hard-to-get underground cave. Start exploring the central area of the Charred Pass to find the small water tank pictured on screenshot 1. Jump in and dive. After you reach a small cave, make your way up. Apart from the stone, the cave also hides and treasure chest with some random loot.
2) You can find the stone near the entrance to the Scar, one of the optional dungeons of the game, located in the south of the Charred Pass. Stand in front of the entrance, turn around and locate the damaged pipe illustrated above.
FJORD (FORGE LANDS)
1) The stone can be found in the temple in the north-eastern part of the Fjord (screenshot 1), which you can get to by following a narrow path. Go inside, turn around the check out the area above the entrance.
LOST TEMPLE (FORGE LANDS)
1) The stone is in the western part of the Lost Temple, in the spot where you can climb to get to the second level (with two balconies connected by numerous vertical beams). It's the same area where you also find a Book of the Dead page.