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Ask Dr. Knowledge

What is the science behind quartz crystals?

February 8, 2010

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I know people who are really into crystals, and while I don’t believe in all this psychic stuff, I understand there is something special about quartz and “transforming energies’’ that the New Age people use to justify their beliefs. What’s the real science?

Quartz is an extremely common mineral (the second-most-common after feldspar). The beauty of clear quartz crystals, together with the relative ease with which one can find them, is doubtless what makes them so popular.

In addition, quartz crystals do have technological applications that are related, in a sense, to transforming energy. In technical terms, quartz is piezoelectric, meaning it can transform energy from one form to another.

If any mechanical pressure is applied to a quartz crystal, a voltage will appear across it, which means it can convert mechanical forces into electrical signals. This made it useful in things such as microphones and phonograph needles in earlier days, though now there are better materials for these applications - and, of course, few people still listen to records.

Alternatively, if you put voltage across a quartz crystal, it will change shape a little. In other words, it can convert electrical signals into mechanical forces. The effect is small, but is useful, especially in making quartz oscillators.

The idea is that you can think of a bit of quartz as a sort of tuning fork that vibrates when struck. That vibration will eventually die out, but if you take the voltage the quartz crystal makes and amplify it (this will cost you some energy from a battery, say), you can then take that voltage and feed it back to the crystal to change its shape at the right moments to keep it vibrating indefinitely. Such an oscillator can be very stable and is the basis for all sorts of electronic devices that require precise standards of timing.

Quartz also finds applications in optics because of its high strength and melting point, compared with glass, and its transparency to a much wider range of ultraviolet light.

Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to drknowledge@globe.com or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.