Simplify the following text for a Grade 4 native English-speaking person.
Original: In the Udden-Wentworth scale ( due to Krumbein ) , silt particles range between and mm ( 3.9 to 62.5 Î 1\/4 m ) , larger than clay but smaller than a sand .
Simplified: Silt particles range between a and mm ( 3.9 to 62.5 Î 1\/4 m ) , larger than clay but smaller than a sand .