How much obsidian can a diamond pickaxe with efficiency 1 mine before breaking?

How many blocks of obsidian can I mine with a diamond pick with efficiency 1 before it breaks? (starting with full durability)

Efficiency doesn't impact the durability of items. Thus, a diamond pickaxe with this enchantment has the same amount of uses still - 1561 blocks.

Pickaxes have different amounts of uses based on the type:

Wooden: 59
Stone: 131
Iron: 250
Golden: 32
Diamond: 1561
Netherite: 2031

Durability:

For block-breaking tools, a use is counted only if a player completely breaks apart one block or hits a mob.

For Pickaxes:

• Breaking a block that breaks instantly counts as 0 uses.
• Breaking other blocks counts as 1 use.

Using a tool properly maximizes its durability. Assuming a player uses a tool appropriately, the maximum durability for a Diamond tool is 1561 uses.

So you will be able to mine 1561 blocks of Obsidian.