Gnomedium

Gnomedium is an easter egg block with no special functionality. It is stronger than Obsidian and requires a Diamond Pickaxe to mine. Its image is taken from a YouTube video.

Crafting
It is crafted with 4 Coal Blocks in the corners, a Diamond Block in the middle, and 4 Iron Blocks in the remaining spaces. This will give you 9 of the block.