Concentrated gold rocks can only be found in the Living Rock Caverns located north of the Dwarven Mine. They require a Mining level of 80 to mine ore from them and give 65xp per ore mined.
Concentrated gold rocks will give 1-3 gold ores at a time. If wearing Varrock armour, multiple ores will be mined even more frequently displaying the message "Your Varrock armour allows you to mine an additional ore", and "you manage to mine two (or three) gold ores!" when mined on your own. Gems cannot be obtained from this type of rock. Unlike all other rocks these do not run out of ore, and instead they are collapsed by the stomping and fist pounding of the living rock creatures.
Recomended strategy: Go to the semi-official world for mining, world 84. If possible use a Lava titan familiar. They provide a +10 Mining boost, which greatly speeds up mining; however, this bonus is invisible and does not allow you to mine the mineral deposits at a lower level.
They are decent experience, at about 50-60k experience per hour and can be a money making method for high level players because the rocks are very close to a deposit box.
It appears that the more people who are mining the rocks, the less often they will collapse.
This is a dangerous area as all of the monsters are above level 120 and are aggressive. To reduce the amount of damage, a group of players could work together.
Low level players may find it easier not to worry if the living rock protectors kill them. With the death respawn set in Falador, they should have plenty of time to make it back to the mines and retrieve their items.
The unofficial world for mining the gold rocks is World 84, as well, many people mine on World 2. It is recommended for lower players to mine the gold on these worlds, as it is less likely that they will get attacked, since there will be a lot of people mining.