The sparkling ring has come to symbolise the betrothal of millions of affianced couples. But, as the millennium nears, the diamond industry seems to be not so much enjoying a whirlwind engagement as to be locked in a shotgun marriage with a frees-pending, unpredictable debtor - the US economy.

Gemstone sales figures due on June 22nd are expected to disclose even greater dependence on the US market than was the case at the end of last year. Halving of demand from Japan and the Far East in the two years since the economic meltdown has left the US as source of nearly 50 per cent of all sales.

This may change as continental Europe edges out of recession. But timing is everything: a Wall Street crash ahead of a European pick-up would leave the industry in disarray. The half-year figures due later this month will show roaring demand from the US but, being historical, will not reflect any fall-out from the recent tumble in the previously popular Internet stocks.

A survey on Tuesday by the Bloomberg news agency found diamond analysts expecting the most recent auction, or "sight", held by the Central Selling Organisation (CSO) to shift one-third more gems than at the same time last year.

But the analysts were unanimous in naming the US as the growth pole in the diamond world. In 1996, Japan and the Far East took 40 per cent of all diamonds, Europe and the rest of the world 20 per cent and the US 40 per cent. The collapse of the "Asian miracle" transformed that; by the end of 1998, the US share was 45 per cent and rising, Europe and the rest 20 per cent; the Far East 20 per cent, leaving a 15 per cent hole in demand. CSO sales in 1998 dived 28 per cent to $3.4 billion (€3.26 billion).

Analysts are expecting a bounce during the first half of this year to between $1.9 billion and $2 billion, from $1.7 billion during the first half of 1998. This is a much jollier picture than could have been predicted at the end of last year. But, according to one Johannesburg analyst: "The big story is in the US."

Dependence on one market is especially worrying when that market is borrowing heavily to finance its love of fancy goods. On Monday, the official statistics showed the personal indebtedness of Americans rose by $3.7 billion in April to yet another record, $1,335 billion.

It is not only over-reliance on big-spending Americans that takes some of the sparkle from trading figures. The CSO and its parent company, the De Beers mining group, is paying a hefty price for propping up the value of the world's stones. The CSO operates a stockpile, but during the gyrating 1990s there was more buying than selling, with the result that the stockpile stands at a record $5 billion. The combination of an overheated US market due for a bucket of cold water and a mountain of unwanted product suggests not so much a loveless marriage between the US and the diamond business as two drunks propping each other up.