On the Black Sea coast of Georgia, in Ureki and Grigoleti, there is a special sand, medicinal according to the local population. People come here to be treated for back and joint pain. Advertising brochures explain this by the healing properties of the magnetic field that forms around the particles of magnetite, in which these sands are rich.

The sand on these beaches is black. Its colour is given to it by iron, mainly the mineral magnetite and its relative titanomagnetite. These are heavy minerals, and it is precisely their heaviness that gathers them: waves and currents carry away the light quartz, while the dense ferrous grains remain and accumulate in the surf zone. Such beaches exist in New Zealand, California, Japan, Chile. In the resort sense the most famous ones are the Georgian.

Magnetite really is used in medicine. Magnetite nanoparticles are introduced into the body and activated by an external alternating field. They are the basis for magnetic hyperthermia of tumours, targeted drug delivery, contrast for MRI (Włodarczyk et al., 2022)¹.

On the healing action of weak magnets there are two opposing opinions in the medical literature.

The review by Fan et al. (2021)² collected 28 studies with a normal control: an analgesic effect was shown by about two thirds of the works on humans and by all the works on mice. In animals the picture is even more convincing. Morris and Skalak (2008)³ induced inflammatory oedema of the paw in rats and applied a magnet: a field of moderate strength, applied soon after the onset of inflammation, reduced the oedema by a third and more. Interestingly, in their own experiments the field did not merely improve blood circulation, but evened out vascular tone: the dilated ones narrowed, the narrowed ones dilated, and both came to normal.

At the same time the large meta-analysis by Pittler, Brown and Ernst (2007)⁴ concluded that permanent magnets cannot be recommended for pain relief. Cochrane reviews assess the quality of the evidence as very low. The most graphic experiment is a simple one: magnetic insoles were compared with insoles ordinary in appearance but not magnetised, in heel pain (JAMA, 2003)⁶, and no difference was found.

Such discord is partly explained by the methodologists. Colbert⁵ and colleagues showed that in many trials the dose of the field itself was not properly measured, and in animals the effect works within a narrow window: too strong a field does not act, one applied too late does not act. That is, part of the negative results may be not «the magnet does not work», but «we missed the regimen».

But what is clearly explainable is two things – the influence of heat and of heaviness. Iron makes the sand not only magnetic. It makes it dark and heavy.

Heat

Dark sand heats up more strongly in the sun, this is obvious. Less obvious is the second thing: magnetite stores heat well and gives it off slowly, so much so that in engineering it is used as a material for heat accumulators. On the body this is felt as a deeper, more even and longer warming than from ordinary light sand of the same temperature.

Weight

Magnetite is approximately twice as dense as ordinary sand. This means that one and the same layer over the body presses approximately twice as strongly. A sand bath of magnetite is, in essence, a heavy blanket, which moreover fits itself to the shape of the body.

Thus the healing effect of the beaches of Ureki and Grigoleti is quite real. In the first place it comes from the special, deep and prolonged warming and the influence of a soft, even pressure, in the second, from the insufficiently studied but clearly present influence of a weak magnetic field.

Beach nidra yoga

I have thought up one more way of using this astonishing sand for treatment – beach nidra yoga.

Nidra yoga is a practice of deep conscious relaxation: a person lies in the shavasana pose and gradually lets go of the body, remaining conscious. And so that the body should really relax, it needs to be fully supported: a pillow under the head, a bolster or a rolled-up blanket under the knees, in order to release the lower back, a small pad on the eyes, a rug on top. There is even a classic device, a little bag of sand on the belly for deeper relaxation, that is, the idea of weight has been present there for a long time.

The logic is simple. Any part of the body that is not supported forces the muscles to hold it, and that means to remain in tension. Remove this work, and the muscle relaxes. I use magnetite sand for this: I build from it a bolster of the needed height exactly under the tense spot, and the loose mass fits itself to the area, repeating its shape, which a rigid bolster is not able to do. And here again the same two factors come together: the support removes the muscular effort, and the weight of the sand adds that very soft deep pressure. Both work in one direction, towards relaxation. The effect of nidra yoga itself has also been measured: after the practice heart rate variability rises, that is, the nervous system passes into a calm regime (Markil et al., 2012)⁹.

And moreover, doing all this on a beach with sand rich in magnetite is far more convenient. The grains of magnetite are dense, with crystalline facets, and therefore cling to one another better than the rounded quartz ones; magnetised grains in addition attract each other slightly. Such a heavy heap is harder to blow away with the wind. So a bolster of such sand really does hold a little more confidently.