A Block of Necromite Ore in the Ground
Necromite is the diamond of the Nether. It is collected from necromite ore which is found extremely rarely. The necromite ore drops one Necromite Gemstone when mined with an iron level pickaxe. It can be crafted into swords, armor, tools, a block, and the execration table. It's based around withering, so a Necromite Sword does withering damage, and the Armor gives withering immunity. A Necromite Pickaxe can mine Obsidian. When the necromite tools are cursed in the execration table, then they all (shovels, pickaxes, axes) become able to inflict wither damage, and the withering inflicted by the necromite sword when cursed will be twice as powerful. The necromite sword is slightly less powerful than diamond, doing 6.5 damage rather than 7.
A Player with the Necromite armor and sword