By Mark Sanders
Europe business reporter
Antwerp is the capital of the global diamond trade
It's gripped gently between tweezers and is worth millions in almost any currency you'd care to choose.
The stone I'm looking at is about the size of a walnut, and it's being assessed at a laboratory in Antwerp, Belgium, so it can be given the equivalent of a diamond identity card.
A certificate will be issued confirming authenticity, and recording its essential characteristics, or the 4 Cs: carat, colour, clarity and cut.
I find it difficult to take my eyes off the 30 carat monster, but for the people grading the diamonds it's another day at the office, and music from a radio drones on in the background.
We're told later by a diamond dealer that the stone should fetch up to $5m (£3m), and that's wholesale.
Antwerp has certainly secured its place as capital of the diamond trade - 80% of the world's rough diamonds and 50% of all polished stones pass through the city. But these are hard times for diamonds.
Philip Claes says the industry is optimistic
"Diamonds are a luxury product, one of the first things that consumers drop from their list," says Philip Claes of the Antwerp World Diamond Centre (AWDC), which represents the industry.
"We have been hit quite hard by the economic and financial crisis."
In the first four months of this year, imports of uncut diamonds to Antwerp fell by 45% compared to 2008, and exports dropped by 30%. For polished diamonds, import and export volumes were down by 32% and 28%, respectively.
The coming months are very important for Antwerp, as jewellers prepare to buy for the Christmas shopping period.
"50% of all polished diamonds are sold in the US, most of them during that period," Mr Claes tells me.
"The predictions are that it will be better than last year, people are optimistic, but a full recovery won't be before the end of 2010."
We talk as he shows me around the Beurs voor Diamanthandel, one of Antwerp's diamond exchanges.
Its huge windows are to catch the clear northern light so traders can assess the diamonds on offer.
They've been doing deals at this exchange since 1904, but with some traders now preferring to do business away in company offices it's also something of a social club.
The Beurs voor Diamanthandel is an institution based on security and trust.
Looking at the lost property board I see several notices saying "found, one stone". It's apparently all too easy for the occasional diamond to drop from a table unnoticed.
Antwerp has had to adapt over the years as globalisation has shaped the industry. In the 1960s the Antwerp area was home to about 30,000 diamond polishers; today there are only 1,000 left.
Traders also use the diamond exchanges as social clubs
Most polishing is now done in other parts of the world where labour is cheaper.
I'm taken to the seventh floor of an anonymous looking building in Antwerp's diamond district to see how rough diamonds acquire perfect brilliance.
At Meylemans & Somers Diamondcutters it looks and sounds like an industrial process, with half a dozen men bent over noisy polishing equipment.
It takes the polishers, each with at least 10 years experience, about four weeks to make a diamond truly sparkle.
At Meylemans & Somers they've managed to resist competition from elsewhere in the world because they specialise in polishing large stones.
"We're talking about huge values, so the cost of manufacture is not that important," says Dany Meylemans.
"Of course there's the low cost of India and China, but we're sitting in the heart of Antwerp.
"We're very close to the owners, and they see the manufacture and their stones every day, we discuss the process and they can change the plan. When you're in India or China it's much more difficult to do this."
To deal in diamonds you obviously need access to a lot of cash, and with the recession biting the industry has had to develop a new way to secure credit.
Raj Mehta says the industry expects the Flemish government to help
The banks have now agreed to accept diamonds as collateral so that Antwerp's diamond trade can access new credit of up to 1bn euros ($1.4bn; £856m) for two years.
The AWDC has also asked the regional Flemish government to support the trade in the form of a temporary additional guarantee of 200m euros.
"Like in every other industry, governments have come into the picture and have helped industries," says Raj Mehta, senior vice president of the diamond group Rosy Blue.
"Antwerp does deserve help and the industry expects it will come."
Before the crisis, about 8,000 people were employed in Antwerp's diamond sector, and indirectly a further 26,000 jobs relied on the trade. It's estimated that about 1,000 jobs have been lost because of the downturn in diamonds.
Mr Mehta stresses that diamonds are an important part of the social and economic fabric of the city. Antwerp has been a trading centre for diamonds for more than 500 years.
"History is very important, the prestige, and there's a lot of employment here," he says.
"To keep a good part of the economy of Antwerp, this [help for the industry] will be an important thing for the government to do."
De Beers first used the advertising slogan "A diamond is forever" more than 50 years ago. "Fewer, better things" is now its message for these straitened times.