What would be more "green". A driveway of concrete or a driveway of marble chips?

I live in a city that proclaims itself to be "green". They recently cited me for too thin of a pebble driveway (which it was). I added 3 yards of 3/4"- 1 marble chips. They then said this was against code. It had to be concrete or paver. What are your thoughts?