minecraft-assets/data/minecraft/recipes/diamond_from_smelting_diamond_ore.json

{
  "type": "minecraft:smelting",
  "category": "misc",
  "cookingtime": 200,
  "experience": 1.0,
  "group": "diamond",
  "ingredient": {
    "item": "minecraft:diamond_ore"
  },
  "result": "minecraft:diamond"
}