1) Crunchy stuff in a walkway 2) Small rocks in a walkway 
Gravel about the size of a pea. Used a lot in driveways and walkways.
A commonly used term for 10mm or 20mm single size gravels, particularly from marine sources where material is naturally more rounded.
Portion of concrete aggregate passing the 3/8' sieve and retained on a No.4 sieve.
Screened gravel the particle sizes of which range between 3/16 and 3/8 inch in diameter.
Pea-size rocks all over the trail or road making it very hard to ride over/through.