Magnets are great, but...

A Yemeni gem dealer was jailed after his claim that an onyx he owned emitted a magnetic field powerful enough to deflect bullets was deemed fraudulent.

Dr `Fathalla Hamed, holding an instrument for measuring electrical fields, says an incredibly strong field would have to be present to deflect a bullet.

Had the hi-tech tests vindicated him in a Dubai court, a Yemeni gems dealer's so-called "bulletproof" stone would have been enough to make James Bond jealous. While the fictional British spy merely brandished a watch capable of radiating a super-strong magnetic field to repel bullets, the precious-gems dealer arrested for fraud in Dubai made the same claim about a supposed magnetic onyx he tried to sell for Dh1.8 billion. Before his conviction in June, the pedlar claimed that his rock created a magnetic force field that protected the user - or, in his case, a test sheep - from flying bullets. While his defence was more science fiction than science, electromagnetic forces can be incredibly powerful, scholars of geophysics concur. Electric currents in the Earth's liquid outer core create a magnetic field as the planet rotates. Rocks acquire magnetism when volcanoes spew magma, which contains magnetic minerals such as molten iron from deep within the Earth. When the magma cools to form igneous rock, the magnetic properties remain frozen in the hardened rock. As it happens, Yemen - where the disputed onyx was purportedly discovered - has 13 active and extinct volcanoes. Still, a geologist who studied flood volcanism in the country for 18 years doubted that the area's volcanic eruptions would have given rise to such a "uniquely special" onyx. "There's a lot of volcanic rock in western Yemen and most of the mountains around the Red Sea have volcanic rocks that are about 30 million years old, but I don't know of any special properties they might have," remarked Martin Menzies, who is now a professor in the earth science department at London Royal Holloway College. Certain areas of the Earth, however, have been identified as magnetic hot spots due to the crashing of tectonic plates underneath the Earth's crust. The magnetism becomes evident in stripes on the mid-Atlantic Ridge due to molten rock that is forced up from the mantle after the tectonic plates crashed. Some archaeologists have also studied so-called "ley lines", or alignments of places of geographical interest that can often stretch for several miles between markings. Conspiracy theorists believe that UFOs use ley lines as travel routes and that the ley lines radiate magnetic or mystical energy. The most infamous ley line, the Rose Line, was popularised in the Dan Brown novel The Da Vinci Code. It is believed the Rose Line formed a line of magnetic force that travelled through the prime meridian connecting the Earth's north and south poles. "The earth itself acts like a reactor, so rocks can produce magnetic fields," said Maamar Benkrouda, the head of the physics department at UAE University. As for whether rocks can produce an "invisible shield" strong enough to alter the trajectory of a fired bullet, Mr Benkrouda was unequivocal. "Impossible," he said. "That rock would require very specific conditions: you would have to have very cold temperatures first of all - less than minus 250 Celsius and helium or nitrogen to get to that low temperature, and then you would need superconducting materials working through an electric current," he said. Magnetic fields do have at least one military use. Navies look for magnetic anomalies underwater to spot submarines that may skew the Earth's natural magnetic footprint. Scientists measure magnetic conductivity by units called Tesla and Gauss, with 10,000 Gauss equalling 1 Tesla. A magnet on your fridge measures about 20 Gauss. Superconductors, however, occur when metals are cooled to such low temperatures that the materials no longer have any electrical resistance. Often, these "critical temperatures" must dip somewhere around absolute zero (-273 Celsius) until the lack of electrical resistance allows electrons to flow freely through the metals. It is through the power of superconducting magnets attached to a rail line that Japan's famous ultra-fast maglev trains are able to levitate. By inducing a magnetic field with a superconductor, the train is able to "float" on a magnetic field powered by the repulsion of two magnetic fields. To reduce friction, thus increasing speed, the train floats on a layer of magnetic force allowing a train to exceed 580 kph. In technologies like magnetic resonance imaging (MRI scans), which use superconducted magnets to show images inside a patient's body, a built-in cooling apparatus required for superconducting magnets (usually powered at 0.5-tesla or 2-tesla) can show images inside a patient's body. Mr Menzies said that although a strong enough or dense enough piece of onyx or agate "could indeed be struck by a bullet and act to deflect the bullet", he dismissed the idea of an electromagnetic force-field as "nonsense". Experimentalist Fatthala Hamed, who works at UAE University's physics department, also noted that bullets are typically made of lead or a lead alloy that has no magnetic characteristics. "Even if it had a strong field, this would not slow down the bullet because bullets are not made of magnetic material," Mr Hamed said. Given the velocity of a flying bullet, there would also need to be a resisting force in the opposite direction to slow it down. "I assume there were no strings attached to this speeding bullet," he said. Haydar Baker, a geophysicist at UAE University, said there was no natural magnet he knew of that could be so powerful. Of course it depends on the size of the rock. But something like a 10 centimetre-long magnetite rock will pull a nail from 10 or 15 centimetres away," said Mr Baker. "You can imagine how strong a field would have to be to pull something weighing 50 grams, let alone a bullet at such a speed." Investing in any so-called "bullet-deflecting rock" would not be wise, Mr Baker concluded. And in the case of the Dubai gem dealer now serving time, he said the shop owner's testimony in court that he successfully tested the onyx at point-blank range four times on a sheep in front of witnesses was hard to believe. "From a technical opinion, I don't think it's true," Mr Baker said. "If this rock exists, the first to buy this rock will be the army. All the armies in the world will want this magic rock." @email:[e-mail]