There are also other terms that can be used depending on the context:

* Sediment: This term is used to refer to any loose material, including rock fragments, that has been transported and deposited by natural processes like wind, water, or ice.

* Clasts: This term is more specific and refers to rock fragments that have been broken down from larger rocks.

* Sand: This refers to grains of rock that are between 0.0625mm and 2mm in diameter.

So, while "grains" is a general term for tiny pieces of rock, the specific term you use will depend on the size, origin, and other characteristics of the rock fragments.