Glass, book 2: Sea Glass
Maria V. Snyder2009

Like the colorful pieces of sea glass washed up on shore, Opal has weathered rough waters and twisting currents. But instead of finding a tranquil eddy, Opal is caught in a riptide. Her unique glass messengers which allow instant communication over vast distances have become a vital part of Sitian society. Once used solely by the Councilors and magicians, other powerful factions are now vying for control. Control of the messengers equals control of Sitia. Unfortunately that also means control of Opal. If that isn’t enough of a problem, Opal’s determination to prove blood magic is still being used is met with strong resistance. The Council doubts her, her mentor doubts her, and even her family is concerned. When her world is turned upside down, she begins to doubt herself. In the end, Opal must decide who to believe, who to trust, and who has control—otherwise she will shatter into a million pieces and be swept out by the tide.