This page of the guide to Assassin's Creed Valhalla Dawn of Ragnarok contains the location of all the Uncut Gemstones in the Gullnamar region.
Location: southern part of the map, near the edge of the region.
This gemstone is located under a small waterfall. You will reach it without any problems. There are no enemies or wild animals around that could cause you any problems.
The Gem is located in a cave in the northern part of Uldar. To get to it, follow the straight path until you have to squeeze between the walls. Do this and you will see the gemstone and the white aura around it.
Location: west of Jordber hut
In order to reach this gemstone you must climb the stone statue. Just beyond the sword is a small gap that you must enter. That is where the gemstone is hidden.
Location: Northern part of the location, on the border with Svaldal
This gemstone lies at the bottom of the river. Dive in to get it. This should not be a problem at all.