How do you get power gems in the legend of Zelda phantom hourglass?

there is an island not charted on the map that has a spring if you have ten power gems press a in front of the spring a voice will say wich gems do you have present select power if you have enough your power spirit will get powered up and you can equip him on the collection screen.this islan is on the bottem left on the screen and is in between three boulders and you cant see it on the map so you have to find it and then it will be charted on the map.hope this helps :>