Gemworld (duology)

Summary
From the back cover (Book One): Dazzling to behold, Gemworld is one of the wonders of the Federation: an artificial world composed entirely of crystal, its atmosphere held in place by a sophisticated network of force fields. Home to a half dozen different sentient races, this singular world is a low-gravity playpen of mammoth spires, endless fractal staircases, gemstone arcs, and dazzling prisms, oil carefully nurtured by the planet's many inhabitants -- until now.

Lieutenant Melora Pazlar, who previously served on Deep Space Nine, is currently stationed aboard the Starship Enterprise where an urgent telepathic summons alerts her to the danger threatening her homeworld.

The crystals that once sheltered her people, and several other alien species, are now growing at a vastly accelerated and uncontrollable rate, wreaking havoc throughout the planet. Captain Picard orders the Enterprise on a rescue mission to Gemworld, but they arrive to find a world in chaos -- and an unexpected menace that traps the crew of the Enterprise along with the fragile civilization they hoped to save!

From the back cover (Book Two): Sparkling like a three-dimensional snowflake in the depths of space, Gernworld once was one of the Federation's greatest marvels. Six different alien races coexisted peacefully on an artificial world composed entirely of crystal -- until the very substance of Gemworld began to multiply out of control, tearing the world apart. Now the entire planet -- and the Starship Enterprise as well -- faces total destruction.

The only way to stop the disaster is to turn off the vast network of force fields holding Gemworld's atmosphere in place, but to do so will require the cooperation of each of the planet's half dozen alien civilizations, one of which sabotaged Gemworld in the first place. With time running out, Captain Picard and his crew, including a lovestruck Lieutenant Barclay, must embark on a hazardous trek across the dying planet to find and unite the chief engineers from many strange and exotic races -- while watching out for a mass murderer determined to destroy a world!