Please provide more context! What kind of big rock are you thinking of? Is it:

* A specific rock formation with a name? (e.g., Uluru, Half Dome, Stone Mountain)

* A type of rock? (e.g., granite, basalt, limestone)

* A rock used for a specific purpose? (e.g., a cornerstone, a boulder in a garden)

Once you tell me more about the rock, I can give you a more specific answer!