"I have been working with quarts and a few other minerals for something I have been working on for a few months now.

             Quartz has a property where it responds every 1 second to the Earth's magnetic field. Which is why it is used in watches and other time pieces. It was also used (as well as Mica) in computer chips before being replaced by other silicone compounds. Quartz if put under mechanical, electrical or magnetic pressure will discharge an electric current equal to that pressure.  Likewise when that pressure is released it will again release an electrical discharge equal to the first discharge. (As a kid I have taken two pieces of quarts and banged them together hard, seeing a pale green flash of light inside the crystal itself like static electricity) . Now quarts does store its own energy and is possible to record energy signatures within it, however to maintain a permanent record, the energy source would have to be great enough to change some of its crystalline structure.

             Now most regions containing quartz naturally will also have other oxide metals. Iron Oxide was the first metal used for recording music on tapes, then came chromium oxide for its better clarity. Iron generates a magnetic field on its own, though in general it is not a magnet itself. However, by facing north and south and banging an iron rod on the sidewalk, you can create a magnet from that rod. If you then face east and west and strike the rod once more, you will demagnetize it. This however causes the iron to become brittle; the impact re-arranging the ion/molecules in the iron to match the earth's magnetic field, then the second impact causing the arrangement to change again.

             I have found a mineral/rock that is not metallic to not only have a north and south magnetic pole (causes a compass to divert) but also seems to absorb electromagnetic energy and radiates it as if its own.  This is Hematite.

             So if in a mountain region or an area with high crystal, mineral and metal content, combining it as a whole, you would have an Earth energy recorder. Thus a violent death with strong emotions would project high energy levels to this area (being connected to the mineral/metal source by the earth's magnetic field). These electromagnetic vibrations would not just fill the metal/mineral area, but the crystals would vibrate, matching the frequency of the source energy, and record it into the metal oxides/minerals. 

             Now weather conditions (Static electricity, lightning, air pressures) or energy sources (even mechanical, such as remodeling, well digging, earthquakes) can trigger the crystals to discharge their energy into the metals/minerals, creating a play back. The brain and other receivers then experience the playback. The crystal mica is used in condenser tuners for radios.  Sheets of the crystal are separated by sheets of metal. As you turn the tuning dial, the metal plates move out from between the mica, thus changing the electrostatic charge stored, and changing the frequency being received. Being quartz and mica are very much abundant (both natural silicone based), it is quite feasible to say that nearly exact historical events could be stored and remembered by the Earth, or even buildings. Likewise it may be possible that some actual spirits/ghosts could get trapped in a place if surrounded by such a geological area, or perhaps confused as to whether or not it is dead or still alive. 

             Anyway, this is my opinion and a theory I have been working with."