Memory Gem

A small, reddish-brown crystal, Memory Gems are not actually precious stones, but rather a treated sliver of crystalline material.
There are three broad grades of these devices. At the cheapest end of the scale the image is held in the stone in a red-and-black scale, with no true color, and can only be seen by holding the stone to the eye and peering through it. Often these are kept mounted in pendants to keep from being lost.
At the medium grade, the stone preserves a full-color representation of whatever it was exposed to- but can still only be seen by being held to the eye in front of a light source.
And at the highest grade, the largest of stones can be placed in front of a light source (often Lumenstone) will be placed behind the Gem- although a simple flame can be used- to project a full-color image against a wall. Extremely expensive, these are often used as a symbol of wealth as much as an actual tool. Rarely portraits of important people will be recorded this way, though more commonly maps are displayed in this way.
The Sovereign Schola has one of the most famous Memory Gems of all time, a truly massive and priceless cut stone the size of a man's head, mounted in the ceiling of the main library on the ground floor. Upon entering the building, all visitors, applicants, students or instructors walk across an impressively accurate map of the entire world, recording in intricate detail.

Mechanics & Inner Workings

The "exposed" surface of the stone has been prepared with a special mixture. When exposed to a second mixture, whatever the stone is facing will be imprinted on the surface.

Rarity

Common to rare, depending on quality and craftsmanship.

Weight

Half an ounce to half a pound

Dimensions

Half an inch to six inches across