Forge of God
Wow. This book. (Forgive the ratty, beat-up mass-market paperback, but used bookstores are awesome.) Yes, it took me until now to read it, and I regret that delay.
Haunting, at times grim and depressing (so be warned - this is not high action/adventure), but also an achingly beautiful love letter to our precious blue marble and the equally precious humans who inhabit it.