local function generate_ore(name, wherein, minp, maxp, seed, chunks_per_volume, ore_per_chunk, height_min, height_max)
    if maxp.y < height_min or minp.y > height_max then
        return
    end
    local y_min = math.max(minp.y, height_min)
    local y_max = math.min(maxp.y, height_max)
    local volume = (maxp.x-minp.x+1)*(y_max-y_min+1)*(maxp.z-minp.z+1)
    local pr = PseudoRandom(seed)
    local num_chunks = math.floor(chunks_per_volume * volume)
    local chunk_size = 3
    if ore_per_chunk <= 4 then
        chunk_size = 2
    end
    local inverse_chance = math.floor(chunk_size*chunk_size*chunk_size / ore_per_chunk)
    --print("generate_ore num_chunks: "..dump(num_chunks))
    for i=1,num_chunks do
        local y0 = pr:next(y_min, y_max-chunk_size+1)
        if y0 >= height_min and y0 <= height_max then
            local x0 = pr:next(minp.x, maxp.x-chunk_size+1)
            local z0 = pr:next(minp.z, maxp.z-chunk_size+1)
            local p0 = {x=x0, y=y0, z=z0}
            for x1=0,chunk_size-1 do
            for y1=0,chunk_size-1 do
            for z1=0,chunk_size-1 do
                if pr:next(1,inverse_chance) == 1 then
                    local x2 = x0+x1
                    local y2 = y0+y1
                    local z2 = z0+z1
                    local p2 = {x=x2, y=y2, z=z2}
                    if minetest.env:get_node(p2).name == wherein then
                        minetest.env:set_node(p2, {name=name})
                    end
                end
            end
            end
            end
        end
    end
end

minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_alexandrite", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -40)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_amethyst", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -50)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_aquamarine", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -10)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_diamond", "default:stone", minp, maxp, seed+21,   1/10/10/10,    1, -31000,  -300)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_emerald", "default:stone", minp, maxp, seed+21,   1/10/10/10,    3, -31000,  -100)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_garnet", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -70)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_opal", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -60)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_peridot", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -60)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_ruby", "default:stone", minp, maxp, seed+21,   1/10/10/10,    3, -31000,  -120)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_sapphire", "default:stone", minp, maxp, seed+21,   1/10/10/10,    3, -31000,  -120)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_topaz", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -80)
end)
minetest.register_on_generated(function(minp, maxp, seed)
generate_ore("birthstones:stone_with_zircon", "default:stone", minp, maxp, seed+21,   1/10/10/10,    4, -31000,  -70)
end)