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Crystal woo refers to a seemingly preternatural ability to make people assign all sorts of ludicrous powers to crystals. The folklore of many cultures as well as modern new age medicine claim that crystals have special powers or energy. This includes pretty much everything, from healing, to protection, to "focusing energy", "directing energy", "aligning energy" and so on. Really, there is nothing that woomeisters and New Age salespeople haven't tried to associate with crystals. They look pretty and they have an almost "supernatural" feel to them, due to the regularity of their shape -- ergo they must have something special about them, despite being nothing more than highly aligned mineral structures. Much crystal woo is also based on Native American woo.
The best known misuse of crystals is of course the "crystal ball", which for many self-claimed mystics and psychics serves as a medium for images from "beyond".
A crystal child is like an indigo child but more 'advanced' or something.
First and foremost, despite what some practitioners who use crystals claim, there is no scientific evidence that crystals have special powers or energy. Answers.com sums up the scientific consensus on crystal therapy:
“”Medical professionals place little credence in crystal therapy, attributing any observed benefits to placebo effect. Their skepticism stems from a lack of scientific evidence for the healing effects of crystals, and from differences of opinion among practitioners about how the therapy actually works.
Indeed, IndianReikiMasters.com admits:
“”The main problem in providing hard core scientific data that would be acceptable to scientists at large is that the sensitive equipment necessary to measure these energy changes is not available today...If the energy could not be measured, the effect it had on the human body could be. Therefore, this inductive means of study became our laboratory. Unconventional devices such as dowsing rods were used to measure the expansion or contraction of the body's energy field.
Any powers that crystals might appear to have can be explained by placebo effect, selective thinking, wishful thinking, unconfirmed testimonials, and communal reinforcements.  Proponents admit that observation of the energy in crystals is dependent on one's intention and attitude. Internet sites selling healing and protection crystals commonly acknowledge that they are intended for entertainment purposes only and should not be considered a substitute for medical treatment or common sense.
Selection and use
A crystal may be chosen, it is believed, by handling it and determining intuitively if it "feels right." Joanne Brannan has this to say about choosing a protection crystal:
“”In order for the magical properties of a crystal to provide effective protection, there must be a positive interaction between user and stone. When buying crystals online, a connection to the crystal may be made by focusing on the crystal in your mind's eye, if the connection is there you will sense it.
Crystals have memory, if you hold a crystal and permeate it with love the crystal will remember your love and suffuse any environment where it is with love. Crystals also absorb negative evergy and sometimes need cleansing. To cleanse a crystal it is believed one may wash it, leave it submerged in salt water or a fresh running stream for some time, bury it in earth, or expose it to sunlight or moonlight.  IndianReikiMasters.com explains how to clear and test a crystal before use:
“”The most effective method for clearing a crystal is to hold or touch it with your hand. Repeat the Light Invocation three times. "I invoke the Light of the God within. I am a clear and perfect channel. Light is my guide." By the time you have completed the third repetition, the negative emotion will be gone. Test this for yourself, and ask a friend to help you. Measure his or her energy field using a dowsing rod...and write down your results. Hand your friend a crystal and measure the energy field. Write down your results. Hold the crystal to your forehead and recall a time you felt angry. Hand the crystal back to your friend, and measure the energy field again. Have your friend say the Light Invocation three times out loud, and once more, measure the energy field. Negative emotions cause a reduction in human energy fields. If the negative emotion charged crystal causes a reduction in the measurable field, you know the crystal is holding or storing negative emotions.
IndianReikiMasters.com goes on to explain that after it has been cleared a crystal can then be programmed:
“”Crystals can receive and hold thought forms...Information or commands are stored in the molecular structure of the quartz crystal as magnetic charged data.
IndianReikiMasters.com further asserts that to program a crystal one need only place it on the brow and imagine the desired result.
In order for one to receive the beneficial effects of a crystal, it is believed it may be worn as a pendant or other item of jewelry, wrapped in cloth and placed in a pocket, or kept in a bag on one's person. Crystals may be set on a computer or microwave oven in order to counteract the effects of those appliances or they may be left about the home, work place, or vehicle.
Crystals are believed to be particularly powerful when placed in a geometric pattern or grid. Emily Gems explains:
“”Crystal grids are made by the placement of stones in a geometric pattern for the specific purpose of directing energy toward a goal. The stones or crystals are then charged by your intention and energy.
For dramatic results it is believed a crystal may be placed on a body part or held in the hand.
How they work, apparently
It is believed that crystals possess their power because they are in tune with the Earth. Olga Rasmussen at HealingCrystals.com explains:
“”If we believe that crystals are as much a part of the web of connection as we are, then we can readily recognize that crystals have the ability to act as intermediaries, enabling us to communicate and connect with higher levels of consciousness and existence.
Gems4Friends.com offers a different explanation of why crystals possess their power:
“”The theory is that gemstones carry vibrational rates. By placing these vibrational rates within the aura - your aura's vibrational rates also change.
Norma Buchanan from American Time also has an explanation for us:
“”Quartz is an ideal material to use as an oscillator. First of all, it loses very little energy as it vibrates, so the vibrations are extremely steady. Secondly, it exhibits what scientists call the "piezoelectric effect," meaning that it vibrates in response to an electric charge and, conversely, generates voltage when it vibrates. This quality is central to the way a quartz watch operates. 
IndianReikiMasters.com explains how healing crystals work:
“”The essence of the body is energy. Crystals functions as transformers and amplifiers of various energies into biological energies that rebalance and re-energize our biological system on the cellular level, as well as on our emotional, mental, and spiritual levels. The premise on which this biological transfer of energy is based is that the body is a series of synchronous, oscillating, solid and liquid crystal systems to which our crystal healing techniques are able to transfer energy directly, as from one crystal to another. This transfer of energy aids the system in attaining a certain functional strength in which it can regenerate.
Rasmussen also explains that "quartz crystals can conduct the energy of the healer's thought-forms and patterns."
Various healing properties are ascribed to a large assortment of gems and precious stones. See Gems4Friends.com for a representative list. Note that the vast majority of the listed healing properties are difficult to quantify. For example amazonite is said to improve self worth.
Certain crystals or stones are associated with each of the chakras, or energy systems in the human body. Rasmussen offers this observation on the specific stones associated with the healing of each chakra:
“”If you read ten books on which crystals or stones you should use in healing and balancing the chakras, you will get ten different opinions...Remember that ultimately these stones represent a broad range of suggestions-perhaps much broader than those you have consulted. Ultimately you must learn to cultivate and develop your intuition and see what you are drawn to using.
Note that Rasmussen also mentions studies are being undertaken by "reputable institutions" to verify the existence of chakras, although no such studies are mentioned specifically.
Proponents of these crystals promise protection from evil, negative energies, psychic attacks, psychic vampires, electromagnetic fields, and energy loss. They claim that quartz is an especially powerful protection crystal. For a comprehensive list of crystals and stones used as various protections, see for example CrystalsAndJewelry.com. 
PaganLore.com explains how protection crystals work:
“”...their energy gently deflects negative energy and introduce positive energy that can help us feel better. They will absorb excess energy and boost depleted energy, which will help bring harmony and protect your space.
HealingCrystal.com mentions that when dealing with protection stones "intention" is critical to success and that one should "be clear about what it is you are trying to accomplish, and think of it in positive terms."
- Alternative medicine
- Color therapy
- The Spirit Science is very keen on crystals and happens to sell them too; what a fortunate coincidence!
- "Crystal and Gemstone Therapy: Crystal Dictionary and Metaphysical Meanings". Peaceful Mind.
- "Crystal Definitions." Mountain Gems & Healing Crystals.
- "crystal power." the Skeptic's Dictionary.
- New Agers, mostly
- Though there is not one single non-natural, super natural thing about the shape of crystals. They are as they are because of math and physics
- Crystal Healing at Answers.com.
- crystal power
- Brannan, Joanne E. "Crystals for Protection: How to Create a Crystal Shield." suite101.com.
- Beginners guide to Crystals and Crystal Healing
- "The Science of Crystal Healing." IndianReikiMasters.com.
- "Crystal Grids." Emily Gems.
- Rasmussen, Olga R. "The Healing Power of Crystals." HealingCrystals.com.
- "Crystal Healing: The Healing Properties of Gemstones and Crystals." Gems4Friends.com
- "The American Time Guide to Quartz Watches." http://www.capetowncorp.com
- "Therapeutic Gemstone Properties". Gems4Friends.com
- "Using Crystals for Protection." PaganLore.com.
- Stones for Protection." HealingCrystals.com.
- Silica Dust, Crystalline, in the form of Quartz or Cristobalite (International Agency for Research on Cancer, volume 100C).