There are 9 Goddess Jewels to collect in the game. They can all be found in the Spring Mine on floors 60, 102, 123, 152, 155, 171, 190, 202, and 222. These are the only locations of the jewels in the game. Each jewel can only be found once on the selected floor.
It should also be noted that you MUST have the Shelf from the TV Shopping Network before you can obtain any jewels.
Tip: The easiest way to get the Goddess Jewels to appear is to save before entering the floor with a Goddess Jewel. Go down to the room using the stairs and start to hit rocks. If you are having troubles finding the jewel and are using a lot of stamina, revert back to your old save. That way, you save yourself the energy, and the floor will be reloaded when you load up your save.
It's greatly recommended to bring 8 Elli Leaves. Alternatively, you can bring 3 elli leaves: smash all the rocks while eating the leaves when necessary, then reload the game and go straight to the rock that holds the Goddess jewel, to then save all 3 Elli Leaves.