Concerned over synthetic lab-grown diamonds in the natural diamond parcels of Surat and Mumbai and the subsequent negative impact this was creating on the minds of consumers world-wide, the world's biggest diamond mining company, De Beers, has issued guidelines to its 81 clients, mainly those in India, on how to cope with the influx of lab-grown diamonds into the market.

The company has started to offer specialized machines on rent to weed out synthetic diamonds. De Beers has said it wants to work with industry bodies to identify those selling undisclosed synthetic stones.

"A consumer's desire for diamonds is the only source of value for the industry. And that desire is underpinned by confidence," De Beers CEO Philippe Mellier said last month.

While a synthetic diamond could have a "legitimate place" in the jewellery chain, "passing off a synthetic as a natural diamond threatens consumers' confidence in diamonds and is at best unethical and at worst fraudulent," he said.

The threat from synthetic diamonds, which are grown in laboratories, is real enough for De Beers, the largest producer of natural rough diamonds by value. Recently, a couple of diamond companies in Mumbai had detected synthetic lab-grown diamonds in a parcel mixed with natural diamonds.

The Gems and Jewellery Export Promotion Council has also set up a synthetic diamond monitoring committee to check the influx of synthetic diamonds into the market.

"Since we are into manufacturing big-sized diamonds, we get our small-sized stones cut and polished on job work from small and medium diamantaires. If any of the natural diamond parcels are mixed with synthetic lab-grown ones then our reputation is certainly at stake," a DTC sightholder said.