At this time of the year, many people find themselves looking wistfully at sparkly heaps of carbon atoms, wondering if they can afford them. The answer for most of us is no - or at least it ought to be - as diamonds worthy of the name are always expensive. A "budget" diamond is a contradiction in terms, a lifeless dud of a gem, its sparkle smothered by a poor cut and a plague of speck-like inclusions.
Few of us can afford diamonds scoring high on the classic "Four Cs" criteria of cut, clarity, colour and carat weight. But that's been true ever since the first ones were dug out of the ground in India at least 3,000 years ago. They are, after all, the rare spawn of the Earth's mantle, born hundreds of kilometres below the surface.
Intense pressure and searing temperatures down there can compel carbon atoms to take up the most rigid atomic structure of all: the back-to-back pyramid. For these titanic natural forces to be applied consistently enough to create a decent-quality diamond is unusual enough. For the result to then escape its birthplace and end up on the surface is an event of risible improbability. Yet still it does happen - and when it does, the cut and polished result rightly commands a hefty price-tag.
Yet for those lacking a millionaire's budget, all is not lost. Science has found ways of turning atoms into crystals whose sparkle will match that of top-quality diamonds for a fraction of their price.
Almost 400 years ago, the Florentine priest Antonio Neri described how the addition of lead oxide to glass created crystal capable of imitating gemstones. It's now known that the compound boosts the so-called refractive index and other optical properties responsible for sparkle. Well-cut and polished crystals with a lead content of around 35 per cent can rival far more expensive diamonds with its light-splitting "fire".
Over the years, other form of imitation diamonds have been found, such as strontium titanate and cubic zirconia. Undoubtedly the most impressive of all is moissanite, first identified around a century ago by an eponymous French scientist while studying samples found near the famous Meteor Crater of Arizona. After dissolving a 50-kg chunk of meteorite material in various acids, Henri Moissan identified tiny crystals of silicon carbide, created in the extreme temperature and pressure of the meteor impact. When cut and polished, the crystals turned out to be even more brilliant and full of fire than diamonds - and virtually as resilient.
Yet for decades moissanite was no use as a substitute, being at least as rare as diamond in its natural state, and punitively expensive. That changed when scientists at a small company in North Carolina found ways of creating artificial moissanite, and jewellery made from it began to reach the market in the late 1990s.
Moissanite is not cheap, but with optical properties that put even diamond in the shade, it's certainly no paltry "fake". Even so, such is the misplaced cachet of diamonds that some might feel the need to pass it off as the "real thing".
Chance are they would get away with it too, for its true nature can be revealed only by sophisticated gemmological tests. Certainly those supposed "quick and dirty" tests for the authenticity of diamonds would be of no use.
Take the quaint claim that diamonds will float in a glass of crème de menthe while fakes sink. While it's true that diamonds are much less dense that cubic zirconia, the only way they will float in the liqueur is by adding in a generous slug of mercury.
The truth is that unlike pearls - whose authenticity is revealed by the roughness felt when they are rubbed against the teeth, there's no infallible "DIY" test for diamonds. The nearest thing to one exploits the amazing ability of diamonds to conduct heat. Their uniquely rigid and regular arrangement of carbon atoms allows them to transfer heat ten times more effectively than most metals - and far better than any fake. This makes them feel cold to the touch (which probably explains why diamonds are referred to by gangsters as "ice"). It also underpins the so-called breath test, in which a real diamond exposed to warm, moisture-laden breath fogs over like a shaving mirror, but clears almost immediately, while fakes with much poorer thermal conductivity remain misted over for several seconds.
Moissanite will pass all these tests with ease. Ironically, the biggest clue to its true nature is that it simply looks too good, and even more impressive than the "real thing".
For those really determined to fool their loved ones, there's now another option: "cultured" diamonds, made in the lab. Attempts to make synthetic diamonds date back at least 200 years and the efforts of various researchers to grow crystals from solutions; they all failed. By the late 1870s, geologists had twigged that diamonds must have been born under enormous pressure, but it took another 80 years to recreate the conditions of the Earth in the lab.
The first to announce success was a team based at General Electric in Schenectady, New York, in December 1955. To do it, they needed a so-called anvil press capable of exerting 50,000 atmospheres pressure and temperatures exceeding 1200 C. This hardly lends itself to mass production, and only very recently have synthetic diamonds been produced in bulk with techniques that can apply these conditions to tiny "seed" diamonds.
The result is virtually flawless "cultured" diamonds which can be cut, polished and set into any type of jewellery. Such near-perfection will still set you back a hefty sum, but it will still be much less than half the price of the natural variety. And there's no need to dissemble about its nature: it is unquestionably a diamond.
But is it worth it ? Clearly there's no simple answer. But for those who believe jewellery should be about the breathtaking dance of light among atoms, the science is clear: you're much better off with a fake.
Robert Matthews is visiting reader in Science at Aston University, Birmingham, England