Could be "Hellhole" by Brian Herbert and Kevin J. Anderson
Taken from a review:
General Tiber Adolphus has been exiled to the Deep Zone planet of Hallholme, after his failed attempt at overthrowing the Diadem
Michella Duchenet and the corrupt Constellation government.
Hallholme is a planet in constant chaos and harsh conditions, the
effects of an asteroid impact centuries ago.
During his ten years in exile, Adolphus has been planning for the
day he can declare independence from the Constellation.
Another section talks about the rare mineral/substance:
With the discovery on the [allied] planet Candela of iperion, a
molecule that can be processed to help guide faster-than-light
traveling spaceships, he has been able to set up his own network of
travel, with Hellhole as the initial hub.
How they stumble upon the ancient aliens:
Pools of oily water are discovered that store the collective memories
of the alien race that lived on Hellhole before the asteroid
destroyed the planet.
The Xayan race dissolved their bodies in the slickwater so that their
memories could go on and so that the next life forms that came along
might take on the personalities saved in the pools.
It's part of a trilogy. The second and third (as yet unpubished) books in the series are "Hellhole: Awakening" and "Hellhole: Inferno".
Read excerpts from "Hellhole" (click on ‘Sample’). Or try this YouTube clip from the audiobook:
