Mnemocite Stone
Mnemocite stones are rare magical stones that allow their user to store one memory. These stones tend to appear as small, sharded black obsidian chunks that could fit enclosed in the palm of an average adult humanoid's hand, about the size of a walnut. Normally cool to the touch and nondescript, they appear to give off a silvery, wispy, ethereal magical energy when observed via magical detection. Some mages claim to feel slight tickles and pricks of emotion and sensation when attempting to infuse the stones with some magical energy.
When identified or meditated on over a short rest, an individual can come to implicitly know the length of memory stored in a given stone if one is present. When storing a new memory in a stone that already contains a memory, the stored memory must be of a similar length (within 20% of total time), otherwise the the exchange fails and the user suffers from a level of exhaustion as their mind reels from the attempt. Further, the process scatters incomprehensible bits of memory amongst the memory the user attempted to store, causing them to remember it only in disjointed, clouded fragments. There is no way to discern the specific content stored within a stone until a memory is exchanged.
By spending an hour meditating with the stone, a memory of any length can be stored. Once stored in this way, regardless of the skills of the user, the original version of that memory becomes clouded and difficult to remember accurately, as if recalling a dream. Over time, it fades almost completely. If a memory is already stored in the stone, that memory is swapped for the new one, the old memory being graven into the user's mind in the last moments of the meditation they use to store their own memory.
Any memory graven into the stone is stored with complete accuracy to the original memory of the user. When recalled, the user experiences the full memory condensed into a moment of real-time - all of the sensations, emotions - as if they had lived it themselves from the perspective of the one who stored the memory.
