Numulite can be used as a kind of currency on Fossil Island. There are a lot of things that you can exchange the numulite for, but some are a lot more useful than some other things you can do. The most useful are the following three: You can use them to enter the fish shoal area and the giant seaweed patches underwater, and of course, to charge the ancient wyvern shield.  The fossils you get can be used to build displays in the Varrock museum. This will give you kudos. There are two other things you can do with the fossils. You can go to the mycelium pool and turn the fossils into enriched bones that give you prayer exp. A small fossil will give you 500 prayer exp, a medium fossil will give you 1000 prayer exp, a large fossil will give you 1500 prayer exp, and the rare fossil will give you an impressive 2500 exp.  You can also exchange them for numulite. The fossil collector will give you 100 numulites for small fossils, 200 for a medium and plant fossil. You will get 300 numulites for large fossils and 500 numulites for rare fossils.  You can also charge the wyvern shield with fossils.