Detrital rocks are named according to the size of the clasts that make them up.

Here's a breakdown:

* Clast: A fragment of rock or mineral.

* Detrital rock: A sedimentary rock formed from the accumulation of clasts.

Here are some common detrital rock types and their corresponding clast sizes:

* Conglomerate: Rounded clasts greater than 2 mm in diameter.

* Breccia: Angular clasts greater than 2 mm in diameter.

* Sandstone: Rounded or angular clasts between 0.0625 mm and 2 mm in diameter.

* Siltstone: Clasts between 0.0039 mm and 0.0625 mm in diameter.

* Claystone (or Shale): Clasts smaller than 0.0039 mm in diameter.

So, the size of the clasts is the primary factor that determines the name of a detrital rock.