I have a fondness for The Devil's Heart myself. In college, I wrote a "missing chapter" for the book that revealed the Ko N'ya had been on Earth as the Holy Grail. I was on a Holy Grail kick at the time (I had written a paper in my freshman English class about the myth). The idea, as I remember it, was that it one of its journeys from one Alpha Quadrant power to another, the ship crashed on Earth (creating the Waste Land), and it "ascended" back into space at the end of the Grail knights' Quest. (In other words, another ship recovered it using a tractor beam.) I don't have the story any more -- that was over twenty years ago, and things get lost over time.
I really like that...
It's for me one of those novels I can read, and then months later read again and still enjoy it. It had to me a "film story" which would have suited a huge big budget film with all the little historical bits about the KoN'ya's various journeys through space, especially all that stuff with the Iconians and such.
I haven't got my copy handy at the moment but was the stone part of the Guardian Of Forever?