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There is no shortage of claims that certain crystals block/absorb electromagnetic fields (EMF). Independent of whether EMF is actually harmful, does a crystal on a necklace protect a significant part of your body? See in particular this video.

I would imagine that a giant slab might provide protection, but a crystal necklace?

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    The ads actually call it "electromagnetic frequencies", not "fields", and give examples that are electromagnetic radiation. One might note that visible light is an instance of electromagnetic radiation, and that a piece of cardboard will block it far better than a transparent crystal. One might also note that even if a crystal did block dangerous radiation, it would block it only where the crystal is, the rest of one's body would still be fully exposed. – Ray Butterworth Nov 6 at 13:46
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    I suppose you could construct a Faraday cage out of metal (which is typically made up of lots of little crystal grains) – GordonM Nov 6 at 15:31
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    "Independent of whether EMF is actually harmful, does a crystal on a necklace protect a significant part of your body?" You can't protect against something that isn't harmful. – Acccumulation Nov 6 at 21:58
  • Also somewhat related: skeptics.stackexchange.com/questions/19615/… – Bryan Krause Nov 6 at 23:09
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No. The types of crystals advertised as "EMF blocking" are typically inert minerals which basically have no EM-field by themselves (not magnetic and having no net charge). There is nothing stopping EM waves from reaching your body just because there is some tiny crystal on your neck or wrist or so on. Like you said you would need a sizable shield of crystal to block EM waves and at that point the fact that it is crystal would probably make it worse at doing so, compared to metal or some other conductor.

In general, electromagnetic fields obey Maxwell's equations, and electromagnetic waves obey the wave equation. If there is some EM field at some region of space, in order for that field to vanish, there must be some other EM field generated to cancel the first field. In general, crystals do not generate such fields.

You can read more about the pseudoscientific and debunked properties of crystals on Wikipedia. In a similar vein, this site details the myths surrounding "crystal power."

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    You're right, but you need to cite a source. – Jerome Viveiros Nov 6 at 5:49
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    Welcome to Skeptics! Please provide some better sources than Wikipedia, which is a tertiary source. Perhaps follow up some of the links they provide to give a more direct answer to the claims. – Oddthinking Nov 6 at 6:13
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    Yes, Dapianoman, answering here is time-consuming. But think of it as creating answers that will be read for years to come. Casual no-reference answers (or poor-reference answers) are discouraged for that reason. – GEdgar Nov 6 at 13:01
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    This is sadly one of those questions where every physicist goes like "huh, I'm not going research that, it's stupid", so it may be hard to find actual research to point to. – pipe Nov 6 at 17:00
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    Wikipedia is an acceptable source here because the science is extremely basic. There is no need to cite a peer-reviewed paper to say "radiation travels in straight lines". – DJClayworth Nov 6 at 17:22

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