It's all systems go. The negative-ion air conditioner, negative-ion fan and negative-ion dehumidifier are all plugged in and humming away, dutifully belching out zillions of the negatively charged particles that, their manufacturers say, take on dust and neutralize pollutants around the house.

Outdoors, however, these clunky contraptions are useless against the lurking nemesis, positive ions, which despite the perky-sounding name are said by some scientists to cause sickness and depression in places where they greatly outnumber negative ions.

What to do? If keeping up with the latest health trends matters to you, then load up on jewelry made from tourmaline, the popular "miracle electric stone" said to increase concentration, reduce stress and even cure bad moods by emitting fields of negative ions.

Among the items on offer at major department stores around Japan are bracelets and necklaces of delicate tourmaline chips, sportier rubber anklets filled with a powdered version of the stone, and even straps said to neutralize harmful emissions from cellular phones. Colors range from dainty pink to imposing black, so there's a match for almost any outfit in your wardrobe.

Tourmaline goods are unquestionably chic. But does shelling out anywhere from a few thousand yen to as much as 26,000 yen actually guarantee any health benefits?

Scientists say it's largely a charade.

"There isn't enough data to back up the claims," said Mitsuo Terasawa, a professor of engineering at Tamagawa University and one of many scientists calling for tighter standards for tourmaline products. "These objects don't yield effects simply because they contain tourmaline.

"You can hold an ion counter to some of these bracelets and get a reading of zero," he added. "Or get about the same reading as a lump of charcoal."

Customers, though, are far more concerned with the latest vogue than with researchers' mind-numbing charts and graphs. Like so many other trends in Japan, the recent tourmaline boom started out as an import from the West, where practitioners of alternative medicine have long believed the stone protects against a wide range of maladies.

Though tourmaline jewelry has been on the shelves of Japanese boutiques for years, sales really began to take off in late January, soon after Fuji TV's popular variety show "Hakkutsu! Aru Aru Daijiten (Encyclopedia of Living)" explored the gem's purported healing powers in a one-hour episode.

Experts say it's too early to estimate the total size of Japan's tourmaline-goods market. Even so, one large retailer said tourmaline has become an ingredient in more health-care products than it can count. Meanwhile, a quick survey of accessories gracing the necks and wrists of average Japanese will prove it's become a hit across a broad social spectrum.

For instance, though most buyers are young women, exotic, rosarylike tourmaline bracelets can also be seen peeping out from beneath the cuffs of a surprising number of salarymen.

Shinichiro Fujita, manning the cash register at a jewelry store in Tokyo's Shibuya Ward, is untroubled by the lack of conclusive scientific data. The stone's popularity alone, he said, should be evidence enough of its curative properties.

"At least 20 customers have come back and told me it helped them in some way," Fujita recalls. As if on cue, a customer snaps up a tourmaline saying she's been told it would relax her stiff shoulders.

Tourmaline is a very hard mineral found in deposits all over the world. Its name is probably a derivation of the word turmali, or "mixed stones," in the Sinhala language of Sri Lanka -- a reference to the many colors in which the sparkler naturally appears.

Controversy over tourmaline is nothing new. Its resemblance to other precious gems seems to have been a source of confusion for a long time. Several stones in the 17th-century Russian crown jewels that were once believed to be rubies were later revealed to be rubellite tourmalines.

But what's behind the most recent commotion over the rock? One of tourmaline's unusual characteristics is that its crystalline structure becomes electrically charged when pressure is applied, a phenomenon that can draw airborne ions -- both negative and positive -- toward its poles. Applying heat produces a similar effect on the stone.

Scientists say popular misunderstanding of this trait has given tourmaline undeserved celebrity status, since measurable results don't occur under everyday conditions.

"By pressure, we're talking a whole lot of pressure. Squeezing with your fingers doesn't produce nearly enough," said Hideaki Chihara, professor emeritus of physical chemistry at Osaka University. And the heat required to get a rise out of tourmaline, he continued, is about 100 degrees Celsius, more than twice the body temperature.

All the hubbub appears to have taken many Japanese researchers and government officials by surprise. Spokespeople at various ministries said they were unaware of any conclusive studies on the effects of tourmaline products on the public. And sales have gone largely unregulated by health monitors.

Hiroko Yamana, who is compiling a market report on negative-ion goods for research institute Yano Intelligence, said the biggest -- and perhaps sole -- restraint on merchants is the fear that exaggerated advertising claims will invite the ire of consumers.

That would explain the softly worded ad copy common to many products. "We don't claim that our bracelets can slow the aging process, or anything like that," said Masumi Tairaku, who runs a small-scale supplier of jewelry and other products using tourmaline. "We simply say our bracelets contain 'tourmaline, an ingredient good for the environment.' "

Tairaku said personal experience has convinced her that several tourmaline products do work. For example, she claimed that tourmaline powder poured in the bathtub helped clear up her skin allergy and that treated wraps reduced the swelling in her mother's legs. Still, even this businesswoman was puzzled by the rush for tourmaline trinkets.

"Word got out that the world needs more negative ions, and Japanese people went into a tizzy," she said. "But one really shouldn't put that much faith in bracelets and straps."