Crystal Singer series
The Crystal Singer series is a series of science fiction novels by American writer Anne McCaffrey.
The series is set on the planet Ballybran which is under a permanent biohazard travel restriction. Ballybran is home to one of the FSP's wealthiest, yet most reclusive organizations—the Heptite Guild. Source of invaluable crystals vital to various industries, the Heptite Guild is known to require absolute, perfect pitch in hearing and voice for all applicants, especially those seeking to mine crystal by song.
Novels in the series are: