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, Stone is one of the basic elements you can create by combining specific starting elements. Here's how you can make Stone:

1. Start with the basic elements: Air, Earth, Fire, and Water.
2. Combine Earth and Fire to create Lava.
3. Combine Lava and 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, combining Stone with Air creates Sand, and combining Stone with Stone creates Rock.

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

Let me know if you need further clarification or help with other combinations!