Coldfire, book 1: Black sun rising
Celia S. Friedman1991

For over a thousand years, the colonists of the planet Erna have struggled to gain control over a land prone to seismic instability and infused with a wild, near-sentient natural force known as "the fae." While sorcerers and adepts manipulate the dark and light sides of this power, the Church maintains its stance in opposition to its use. As the dark side of the fae grows in strength, feeding off the nightmares and greed of the minds that are drawn to it, four individuals form an unwilling alliance to battle the source of evil.