Acording to the Indiana-Jones-wiki...
Years later [i.e.: after "The last Crusade"], the elder Jones remarked on the elusive, indefinite nature of the Grail, commenting that the cup discovered by the father-son team was simply "a Grail. But many of the oldest Grail texts, written by the most ancient seers, refer to the Grail as an elixir, as a bread, a powder, gold, or a stone."
Could anyone please tell me, where (i.e. in which novel) this quote can be found? I would be really grateful for help, because I couldn't find the answer via google and my local library hasn't got the Indiana Jones-novels.
The Indiana-Jones-wiki lists the following novels or films, in which the grail appears or is mentioned:
Young Indiana Jones and the Ghostly Riders (Mentioned only)
The Mata Hari Affair (Mentioned only)
The Day of Destiny (Mentioned only)
The Secret Treaty (Mentioned only)
The Rule of Russia (Mentioned only)
Indiana Jones and the Emperor's Tomb (Mentioned only)
Indiana Jones and the Last Crusade (First appearance)
Indiana Jones and the Mystery of Mount Sinai (Mentioned only)
Indiana Jones and the Spear of Destiny
I first thought this might indicate, that the quote should be taken from the "Mystery of Mount Sinai" or the "Spear of Destiny", because they both take place after the incidents of "The Last Crusade". On the other hand, the sources of the wiki-article only list the following items:
Indiana Jones and the Temple of Doom Sourcebook
Close Encounters of the Random Kind (Ambiguously canonical source)
Indiana Jones: The Ultimate Guide
Indiana Jones: The Official Magazine 3
The Greatest Adventures of Indiana Jones