So a meteorite landed in my world but I get hurt when i touh it so can I use dynamite to mine it?
I believe so. Your best bet is to defeat the eater of worlds, and make a nightmare pickaxe, then collect enough obsidian (20) to make a skull. That way you don't get hurt by any fire-natured blocks.
You can get to dark orbs easily with any tier of pickaxes, just buy some "purification powder" from the dryad. This turns the ebonstone into normal stone, allowing you access to the orbs.