The word that describes shapes and sizes of grains in a rock is grain size.

Grain size is a fundamental characteristic of rocks, particularly sedimentary rocks, and is used to classify and describe them. It encompasses both the shape and size of the individual mineral grains or rock fragments that make up the rock.

Here are some common terms related to grain size:

* Shape:

* Angular: Sharp edges and corners

* Rounded: Smooth, curved edges

* Subangular: Slightly rounded, with some sharp edges

* Subrounded: Slightly angular, with some rounded edges

* Size:

* Clay: Less than 0.0039 mm

* Silt: 0.0039 - 0.0625 mm

* Sand: 0.0625 - 2 mm

* Gravel: Greater than 2 mm

Note: The specific terms for grain size can vary depending on the geological discipline and context.