Magnetite is a raw resource under the Metals Metals type of resources.
How to Get Magnetite:
Harvest in the Open World
Skull and Bones – Harvesting ResourceMagnetite can be harvested in resource nodes found in the open world. You will need to use the Pickaxe tool in order to be able to harvest the resource successfully.
To see resource locations on your map, you can click on Track Blueprint while hovering over the item you want to craft. They will show up on Active Item Filters, which will highlight related resources in your map.
Keep in mind that other players can still get these marked resources, in which case it would be best to just move on to the next marked location.