GravelTurtle

function findGravelInSlot()
    for i = 1, 16 do
        local item = turtle.getItemDetail(i)
        if item ~= nil and item.name == "minecraft:gravel" then
            return i
        end
    end
    return 1
end

function detectGravel()
    if turtle.detect() then
        local success, block = turtle.inspect()
        if success and block.name == "minecraft:gravel" then
            return true
        end
    else
        return false
    end
end


while true do
    turtle.suck()
    if detectGravel() then
        turtle.dig()
    else
        turtle.select(findGravelInSlot())
        turtle.place()
    end
end