Pebbles are not made from a specific type of rock, but rather from fragments of any kind of rock.

Here's why:

* Pebbles are formed through erosion: The process of rocks breaking down into smaller pieces due to forces like water, wind, and ice.

* Any rock type can be eroded: This includes igneous rocks (formed from cooling magma or lava), sedimentary rocks (formed from sediment), and metamorphic rocks (formed from existing rocks under heat and pressure).

So, a pebble could be made of granite, limestone, sandstone, basalt, or many other types of rock!