This doesn't work on the XB360, as ZP do not spawn in the overworld near Nether Portals.... yet.... I believe that was a PC version 1.3 update where that started?
Turn your world into something using the Mass Effect Mass Up pack. In that set of textures, obsidian is a white block that looks very much like concrete in builds. I've been playing one world in Mass Effect since the day the pack came out and have spent many, many hours mining obsidian (although I'm probably not up to the 2500-block range yet... maybe half that).
There is a more efficient way to mine obsidian than what you describe... just leave a layer of water on top of the obsidian as you mine. That way, it doesn't matter how the block pops or whether or not there is lava below it. The water will instantly turn any lava next to the block being mined into obsidian as well and the drop never gets burned up. Mining obsidian goes a lot faster when you're not losing any of drops. (This trick is great for mining diamonds as well... I always put water down before I mine a diamond block just in case there is lava nearby and I haven't lost a single diamond to lava in ages and ages.)
Also, use a diamond pickaxe that has an efficiency enchantment when you can. Efficiency IV really speeds up the process A LOT. I never use an Efficiency enchanted diamond pickaxe for mining anything else other than obsidian. That way if I happen to get one at the enchanting table, it lasts a good long time. For mining other blocks in the game, you can get Efficiency quite frequently on iron pickaxes for very few levels of XP, so you don't really need to wastefully use up diamond pickaxes to speed up general mining.
I have a serious problem, every time I come across a lava lake near bedrock during my branch/grid mining activities, I feel this overwhelming urge to completely destroy the lava...
This doesn't work on the XB360, as ZP do not spawn in the overworld near Nether Portals.... yet.... I believe that was a PC version 1.3 update where that started?
There is a more efficient way to mine obsidian than what you describe... just leave a layer of water on top of the obsidian as you mine. That way, it doesn't matter how the block pops or whether or not there is lava below it. The water will instantly turn any lava next to the block being mined into obsidian as well and the drop never gets burned up. Mining obsidian goes a lot faster when you're not losing any of drops. (This trick is great for mining diamonds as well... I always put water down before I mine a diamond block just in case there is lava nearby and I haven't lost a single diamond to lava in ages and ages.)
Also, use a diamond pickaxe that has an efficiency enchantment when you can. Efficiency IV really speeds up the process A LOT. I never use an Efficiency enchanted diamond pickaxe for mining anything else other than obsidian. That way if I happen to get one at the enchanting table, it lasts a good long time. For mining other blocks in the game, you can get Efficiency quite frequently on iron pickaxes for very few levels of XP, so you don't really need to wastefully use up diamond pickaxes to speed up general mining.
"There's your problem." ~ Adam Savage
Well, that is worth a achievement, have fun with Minecraft 360