Letter from Grothendieck to Tate on "crystals"

In the light of past events ("Les Archives Grothendieck"), we now have an "ameliorated" version of the letter:

Cote n° 6. Lettre Tate (mai 66) (Cristaux) : lettre (1966), tapuscrit, notes manuscrites. 1966 - [à partir de 1970].

[scan], and project of transcription [pdf]

See [Analyse] for more.

I don't know if this is of any use.... but I believe that the ideas in this letter were written up somewhat later in this article:

Grothendieck, A. Crystals and the de Rham cohomology of schemes. 1968 Dix Exposés sur la Cohomologie des Schémas pp. 306–358 North-Holland, Amsterdam; Masson, Paris

The article is actually some notes by Coates and Jussila of a seminar by Grothendieck. You can find a copy of the article at chapter IX of this book.