The candlestone / Bryan Davis.

Enhanced descriptions from Syndetics:

nbsp;nbsp;nbsp; The first book, Raising Dragons, plunged two teenagers, Billy Bannister and Bonnie Silver, into mind-boggling mysteries, life or death pursuits, and deadly sword-to-sword battles. nbsp;nbsp;nbsp; In The Candlestone, a mysterious book leads Billy into mortal combat with a powerful dragon slayer. Separated from his friends and finding his dragon traits useless against this enemy, he has to rely on new weapons, a sword and shield he cannot even see. nbsp;nbsp;nbsp; A scientist lures Bonnie to his laboratory with amazing news--her mother is still alive! And he should know; he's her father. He has learned the secret of long life--dragon blood, and he wants Bonnie to help him with his experiments. But first he must send her to retrieve her mother from the candlestone, that strange, paralyzing gem that absorbs light and with it the strength of dragons and their offspring. nbsp;nbsp;nbsp; The candlestone is also a prison that imprisons people who have been transformed into light energy by Excalibur, King Arthur's great sword. When Bonnie enters the stone, she learns that many disembodied souls have fallen prey to the gem's powers, but no one has ever escaped. Her only hope is for Billy to overcome the dragon slayer and find a way into the candlestone, and, more importantly, a way out. nbsp;nbsp;nbsp; Billy and Bonnie face their greatest fears, and they learn to use their strengths, both innate and newly found, as they battle powerful enemies, ancient fiends from times long past, and the horrors of the blackest of prisons, captivity with the walls of unearthly darkness, the crystalline tomb of the candlestone. nbsp;