Obsidian can only be mined with a Diamond Pickaxe, and it takes 9.375 seconds to mine, or less if the Pickaxe is enchanted with any level of Efficiency. Mining by hand takes 250 seconds, and mining with a pickaxe takes 50 seconds; however, neither method yields a block.
You can find more details about mining on the video down below! You can also browse for minecraft servers on which mining is easier.