| Category | Resources |
| Alias | Zuggs Gallstones |
| Type | natural stone |
| Source | abundant, widespread in the Underdark |
Any rock that is radioactive is commonly called a deep rock. The effects of these rocks vary, but prolonged exposure can cause sickness, mutations or even death.
In the Creation War (1486 DE - 8777 DE), an army of dwarves was captured and sent to Cruharr. In this fiery Underdark region, the dwarves were put to work mining deep rocks. The prolonged exposure to these rocks mutated them into a new race called the Azer.
In the Demon Spawn War (8972 GE - 9493 GE), a slave force under Zuggtmoy was put to work in the mines of Siolix. Surrounded by deep rocks, many perished. Those that survived, mutated, becoming the first Fomorians. It is because of this that in some areas deep rocks are called Zuggs Gallstones.
The drow utilize deep rocks to imbue finely crafted adamantine items with pseudo magic. Some deep rocks have a mutating effect on those exposed to it. The mutations often carry on to future generations. Two races that have been "genetically-altered" by exposure to deep rocks are the Derro and the Mutants of Undercity.
Some of the deep rocks beneath Gandûm-Thûr have properties that enhance psionics and help in "opening up" those with psionic potential.
Deep rock can be used to add a special property to magic items. An enchanter with sufficient skill and ingredients can give the item an alignment focus that reflects that of his wielder, such that a lawful good wielder makes the item effective in overcoming a damage reduction of 5/evil or chaos, 10/evil and chaos, and so on. If the creature is true neutral then they benefit from it being able to overcome all damage reductions that are based on an alignment value. The Alignment Focus property adds +1 to the items market price.
A deep rock item that has been magicked no longer has mutative effects.