* Grain Size: The texture of a rock is determined by the size, shape, and arrangement of its mineral grains. Roughness often indicates larger grains, creating uneven surfaces.

* Types of Rocks: Many rocks with rough textures are igneous or sedimentary:

* Igneous rocks (like granite, basalt, or obsidian) form from cooled magma or lava. The cooling process influences grain size, with slower cooling resulting in larger, more visible grains.

* Sedimentary rocks (like sandstone, conglomerate, or breccia) are formed from cemented sediments. The size and shape of the sediment particles contribute to the rock's texture.

* Exceptions: There are exceptions, like:

* Metamorphic rocks (like marble or slate) can have smooth surfaces due to the pressure and heat they experienced during their formation.

* Some igneous rocks can have very fine-grained textures, appearing smooth to the touch.

In summary: While not all rough rocks have grains, it's a strong indicator. The size, shape, and arrangement of these grains are what ultimately contribute to the rough texture.