poke.addicted

To upgrade the Pick Axe, and make it stronger, you first must be at the Silver Mountains. You'll be able to find a Diamond Fragment in there, or in Cave of Darkness. Some of the Demon Soldiers might carry them. The one's who turn into the Clay Ball. The Axe needs that item, I believe 3 or 5 of them, to use, and More Iron I believe. Once you get the Diamond Fragments required, Ussop will upgrade it, and you'll have a Huge Axe, allowing you to enter the Silver Mountains, and other areas. The Rocks which are purple, give you a Metal Plate, which also upgrades the Net to catch Poisonous things. As well as the Fishing Rod with Wood, and Fluff. Hopefully, I answered your question, and then some. Have fun :)