To be honest I think fishing is the easiest way to get crystals. Not gonna lie it’s kinda hard to get leach blood and a bit hard to get tree sap if your new, but fishing is a non threatening life way to get em.
If you are early to mid game then I suggest going up the volcano on the island
(I play ark mobile) as on top it has all the obsidian,metal and crystal you want. The volcanoe is much better than caves to get crystal I think because you dont have to think about all the possible threats as once on top off the volcano I found that there were no dangerous animals. I could suggest building a base their because off all the crystal and material but it would probably be late game
On the island, there is a little mountain near the footpaw I think that has a few small crystal nodes. It isn’t much, but in the early game it’s the easiest source of crystal for spyglasses and water jars