The original site where I learnt about reiki grids is longer available - so here are a few links

http://stores.ebay.com/The-Cosmic-Emporium_Specialty-Mu...fsubZ2QQftidZ2QQtZkm

http://pjentoft.com/f-30-grids.html

Crystal Grids
There are different kinds of crystal structures that are called grids. There are so many kinds and forms that we not going to be able to explore very many of them at this time and will just begin with a general introduction and few simple forms . I usually work with very simple grids rather than the more elaborate and esoteric forms and do not find them any less effective than more elaborate grids or those made with a lot of formal ritual . Your experience may differ.

Some grids are large structures placed on the ground which connects with the ley lines of the Earth which are the planetary equivalent of the meridian channels and other energy channels in people . All the crystal within the Earth can be thought of as being elements of a huge grid . There are groups of people who go around placing crystals in the ground to restore the Earths' crystal grid where they feel that it is broken or disrupted and other groups who feel that this creates disharmony in the the Earth grid. ( I don't know if they follow the first group around taking crystals out or not.) Stone structures at centers of spiritual energy Such as Stonehenge and medicine wheels are also sometimes called stone grids.Some people call the layouts of crystals which are sat within or placed around and over the body, grids.

There are various methods of actually creating grids but most begin with meditation and careful respectful placement of the stones and crystals. Often the stones are placed in clockwise order. People may choose smudge the area and or make offerings to the stone spirits before making the grid or after placing the stones if that is within their traditions.

http://www.rainbowcrystal.com/reiki/crystalreiki.html#sd

The Star of David Pattern

We place quartz crystal points under our massage table in a pattern called the Star of David layout. For this, place crystals on the points of an imaginary Star of David: one each below the head and foot, one each below the shoulders and hips.

We have found that this layout creates a very stable and relaxing energy pattern which seals in the Reiki energy. We also recommend it for meditation.

Hands On

Often clients enjoy holding a crystal in one or both hands during the treatment. You can either let them choose the one(s) to which they are attracted, or make suggestions, such as:

For grounding issues: hematite, tiger's eye, black tourmaline, red jasper, smoky quartz

Anxiety/nervousness: amethyst, rhodochrosite, aquamarine

Love issues: rose quartz (for relationship issues); emerald, for feeling cut off from divine love or one's spirituality

Opening up spirituality: clear quartz, chrysocolla, amethyst