Crystals disseminate, scatter, guide or activate energies almost anywhere in a room or home.  The quality of the crystal is important.  Only flawless faceted crystals made from high-quality material will be effective.  The most popular shapes are round (yin) and drop-shaped (yang).  Applications:  (1) In a window to prevent loss of energy, to disperse negative energies and to energize a room with rainbow colors. (2) Between a door and and window when the door and window face each other, to redirect the flow of energy. (3) In long hallways to slow the flow of energy. (4) On corners or edges to lessen their aggressive energy or cutting effect. (5) To activate energy in static rooms. (6) In small rooms to keep energy flowing. (6) In the center of a room to stabilize and focus energy. (7) Between a door and bed to dissolve a potential conflict.  Crystals need to be cleaned on a regular basis to maintain their effectiveness.  Dustry/dirty crystals produce and reflect dusty/dirty energy.  The size of the crystal should be in proportion to the size of the window/room/hall.  Affirmation to use when placing your crystal: The transformation of energy supports wholeness.  May the messenger of light bring clarity and insight into my life.  Source:  Feng Shui Symbols by Christine M. Bradler & Joachim Alfred P. Scheiner.