Metal is mined from many types of rocks. It is possible to obtain it from normal rocks, but these rocks have a very low yield of metal. Certain rocks hold substantially larger amounts of metal. These metal rocks usually look smoother and more golden than usual rocks. Generally, metal rock density is higher in areas that are dangerous or hard to reach, such as mountain tops, caves, rivers, coves and deep water sources.
In Aberration the golden colored metal rocks can be found, but blue veined black rocks (found in the Luminous Region) also yield large amounts of metal.
The rocks are mined with either a pickaxe, preferably a Metal Pick as it yields a lot more metal per rock, a mining drill, or the most efficient way, with an Ankylosaurus with its Melee Damage boosted, which also makes carrying the mined ore easier. The general mechanics for resource harvesting are presented in Renewable resources. Standard metal rocks take ~1 hour to respawn after being mined.
Metal can be gathered most efficiently using an Ankylosaurus, which also offers a 85% weight reduction of metal when in its inventory, or by using a metal pick. When at mastercraft or ascendant tier, the metal pick is reported to gather just as much metal per metal spawn as the Ankylosaurus.
Below is a list of creatures and tools that can be used to gather metal.
If you have another player with you, they can pick you and your Ankylosaurus up using a Quetzal or Argentavis. They simply then fly you next to metal rocks on a mountain, and you can harvest them without even touching the ground. This strategy allows for higher mobility and higher carry weight since a Quetzal can carry much more than an Ankylosaurus.
Carrying the opposite gender Ankylosaurus provides a mate boost to the one you're gathering metal with, providing a 33% bonus in damage, and thus increasing the yield of metal. This other Ankylosaurus can be a low level so if it somehow clips and falls, you will not have to worry about losing it.
The following creatures reduce the weight of Metal by the listed amount while it is in their inventory:
The Frozen Tooth at 35 latitude and 55 longitude has extremely high quantities of metal rocks at and around the summit. However caution is advised while attempting to descend the mountain, as it is extremely steep and quite easy to fall.
Low level characters can go to a small mountain in the Southern Islets at around 76 latitude and 44 longitude which has a decent number of metal bearing rocks (100+ units with a metal pick) at its summit, along with a small supply of crystal. The eastern side of the mountain is easy to climb and scattered with more metal bearing rocks, and the area itself is fairly benign, hosting mostly low level herbivores with the occasional Raptor or Carno.
Small mineable piles of stone and the small round boulders around rivers and beach shores tend to yield more metal than regular stone nodes. This is much more so if using a metal pickaxe, and can be a great source of metal in a pinch for low-level survivors.