How do I unlock the stone category in Little Alchemy 2?

In Little Alchemy 2, the Stone category is not something you "unlock" in the traditional sense. Instead, you create Stone by combining specific elements. Here's how you can make Stone:

1. Start with the basic elements: Earth and Fire.
2. Combine Earth and Fire to create Lava.
3. Combine Lava with Air to create Stone.

Once you have Stone, it will be added to your collection, and you can use it to create other elements. For example, Stone can be combined with Fire to create Metal, or with Water to create Sand.

If you're looking to track your progress or see what elements you've created, you can check your Encyclopedia in the game. This will show you all the elements you've discovered and help you identify what you're missing.

Let me know if you need further clarification!