"What constitutes the crystal is the most fundamental operation of time. Time has to split itself in two at each moment as present and past...one of which is launched towards the future while the other falls into the past. Time consists of this split and it is this, it is time, that we see in the crystal.
Bergson adds...the crystal constantly exchanges the two distinct images which constitute it, the actual image of the present which passes and the virtual image of the past which is preserved: distinct yet indiscernible.
The crystal lives at the limit, it is itself 'the vanishing limit between the immediate past which is no longer and the immediate future which is not yet...[a] mobile mirror which endlessly reflects perception in recollection'.
The crystal-image is then, the point of indiscernibility of the two distinct images, the actual and the virtual, while what we see in the crystal is time itself, a bit of time in a pure state, the very distinction between the two images which keeps on reconstituting itself."
G. Deleuze, Cinema 2: L'Image Temps, 7th ed. University of Minnesota Press 2003, pp. 81,82, 274 (abridged), italics mine.
