gravel/coarse_gravel

{
    "type": "overpass",
    "name": {
        "en": "Coarse Gravel"
    },
    "query": {
        "6": "(node[surface=gravel];way[surface=gravel];node[surface=pebblestone];way[surface=pebblestone];)"
    },
    "info": "Coarse gravel and pebblestones."
}