You can tell if a rock is an elemental quite easily because they always seem out of place, for example a bright yellow rough stone (the elemental) in the middle of a smooth black mountain. They arent very good at hiding
If you are unsure if a rock is a disguised golem or not, a spyglass shows their name and level even when disguised. Also, when disguised, the rocks often move slightly as you get close, re settling onto the terrain.
If you kill them using a thyla’s gnashed ability then you can harvest their body with an anky. Killed a level 95 and just got 198 stone, 114 Crystal, 134 obsidian, 123 oil, and 78 metal from it. Hope this is useful to someone!! Have a nice day!!! :)