We all have been there. That moment you make the mistake of making obsidian instead of cobble. Well no worries WD to the rescue.
Just a small rule of thumb on gens. Your lava needs to spread to your water. If it doesnt make since it will.
When you build your gen we all know you want at least one space between your lava and water but you actually want two between the lava source and the water source blocks. But if you just place water and then two blocks away place lava your still going to get obsidian. So what are we missing?
The solution for this age old issue is dig a hole 4 blocks wide and then on the second block in that hold dig it out too.
Next place your water on the single block and your lava on the other end. Here is your very first and singular cobblestone gen.
Now i could go in depth and show you the really advanced setups with redstone and such but this is skyblock. Typically you dont get redstone not to mention how espensive they are to build when you must buy your redstone.
Better solution is to simply make a line of these trenches. This will make those pesky server issues go away when your waiting on the cobble to make in the rest of the gen. Now we all know space is not something we have alot of on SB but we have a minor solution to this. just make these side by side and run circles. This is in fact exactly how my SB gets its cobble.
If your still having trouble making a cobble gen then you should check out some on YouTube.