

Well the tree could technically count for earth. For fire you could maybe just use a flame with the silmaril in the middle (would look cool as part of a larger tattoo,in a sleeve or something). Water is tough though! The best I can think of right now is a rain drop. If you could think of a way to make a wave that would fit, since waves have been a huge part throughout the history of ME. Or you could think of a completely different design, a trident or something (no real relation to Tolkien), but then put the silmaril inside of that.
Or you could simply make the silmarils different colors and put them wherever you want. Inside another tattoo or any random place or whatever. Like a radiant blue for water, maybe with light blue light streams coming off of it and the bottom ones turn into little rain drops or something.
If you wanted to scrap the random place idea you could do something like Morgoth's crown and have the 3 silmaril's in there. That might be pretty cool! Assuming you don't mind having the Dark Lord's most powerful symbol on your body....
Different colors why didn't I think of that. I love you Balrogs you never disappoint me.I haven't ever seen a tattoo of a waterfall, could be interesting! I really love the idea of incorporating the trees though. I have to really think about it because I want it on my shoulder which means it's very visible and sometimes not easily covered. I am going to wait until the fall anyways to do anything because there still could be some swimming opportunities yet this year! Fall is my absolute favorite though!
Maybe you could have the silmarils scattered inside of the tree. Like you'll have the tree, and maybe a green jewel in the trunk, a blue one in one corner and a red one closer to the center. Something along those lines. Honestly just throwing random ideas that came to me out there though....