Calcite

Calcite is found in the Mushroom Forest area of Fossil Island It is used with Pyrophosphate on a Mycelium Pool in order to recalcify fossils into enriched bones which can be used to grant prayer xp.

Uses
''So it appears that the mycelium pool can convert fossils into enriched bones via a chemical process. This uses pyrophosphate and calcite, both gained from several places around the island. Whilst the reaction is happening in the pool you must keep your fossils below the liquid level, as they tend to float. If you don’t do this, you will lose some fossils to the chemical reaction. Once done, you can rinse them off and use them to get prayer XP at another location on the island.''

Locations
Several places on Fossil Island