Rust Dust, an item from the Realistic Minecraft idea pack, is obtained when a Rusted Iron Block is mined without Silk Touch. 6-8 are dropped; however, 9 are required to craft the block again. However, Rust Dust is also a food item. When eaten, it restores 0.5 Hunger points, but also gives the player the Nausea effect for 5 seconds.

Crafting Into Iron

When put in a Transmogrifier, 9 Rust Dust will turn into 1 Iron Ingot. This means it requires 81 Rust Dust to craft it back into an Iron Block using this method.