There are two level 5 node areas in Central Thanalan. Bone Shards are in the other node area.
One area is right north of the Steps of Nald gate, which is where you are digging now, but the other is further to the east, against the cliffs east of the Steps of Nald gate.

You can use http://xivdb.com/?maps/43/w1f2-00/Thanalan/Central-Thanalan and check the Mining Points to see where to go.