Osmium Ore (block)

Osmium ore is a mineral block found underground. It's the rarest, and toughest to mine mineral in the Overworld. Osmium ore requires an iridium pickaxe or better to mine, and it will drop one osmium ore item, which are smelted five at a time to get an  osmium ingot. Osmium ingots can be used to craft osmium furnaces.

Natural Occurrence
Osmium occurs from layer 1 to layer 5. It will replace bedrock blocks, making it difficult to find and mine. It will never spawn lower than layer 1, so using osmium to get to the void is not possible. Osmium will spawn in big veins, and one vein should at most cases give enough ores to craft one osmium furnace.