Obsidian is a very powerful mineral, the second thing to Bedrock which is almost impossible to mine, it may be mined in Servers but not in Single Player Mode, unless you are creative. Obsidian is so powerful, it cannot be destroyed by Creepers, TNT, not even Ender Dragons.
NOTE: If you have a Diamond Pickaxe already, don't bother reading what's below. Just skip to the 4th picture.
How to get Diamonds to make a Diamond Pickaxe:
What you need:
-1 Iron Pickaxe
-1 Shovel (Optional)
- Torches to light caverns
Step 1: Find a spot or a cave and dig strait down or light up the entrance, watch out for lava and water pits.
Step 2: Diamonds usually appear just around Bedrock, lava levels and large spaced caverns. When you see Diamond Ores like these mine them with your pickaxe and bring them back to the surface to make your Diamond Pickaxe.
Step 3: In order to make the Pickaxe you will also need 2 Sticks by crafting Wood into Wooden Planks and Wooden Planks into Sticks and then you have your Diamond Pickaxe.
To Get Obsidian:
What you need:
-Torches
-Diamond Pickaxe
-Bucket of Water
Step 1: Go back to the place you got your Ores and look for Lava, if you see no water then use your bucket of water and put it on lava, that way you make Obsidian but be careful, Water can sometimes- Take over lava so you only have water instead of Obsidian, make Stone blocks or make Cobblestone.
Step 2: When you see Obsidian mine them with your Diamond Pickaxe but you will need patience as Obsidian can be taken about 20 seconds to mine with a Diamond Pickaxe, and when you have Obsidian, you're done!