The Dead Lands of Athas
This item is indistinguishable from a cognizance crystal. The crystal is extremely useful for those who have information they wish to store, but wish that it cannot be easily found. A mnemonic crystal can hold a specified amount of information, based on the power of the item. The user waves the crystal over whatever information or data he wishes to store in the item, which is then saved in the device. The crystal contains “pages" of information, and each page filled requires a move-equivalent action. The pages can be filled with spells without paying the 100 gp per page material cost, just like using a blessed book.
A creature wishing to use the information contained within a mnemonic crystal must first attune itself to it. To attune the crystal to its owner requires one hour of meditation with the crystal, after which the user has access to the contents of the item, and may erase information as he desires. The information is accessed at the same speed a user would have read it, including any limitations on language or deciphering the text or spells, if any. Only one creature may be attuned to a crystal at a time.
A typical mnemonic crystal weighs approximately 1 pound, has AC 7, 10 hit points, a hardness of 8, and a break DC of 16.