Kate Winslet helps Gem with trend for yellow diamonds

They might not have helped her marriage, but Kate Winslet's love of yellow diamonds - which she sported at the Oscars - seems to have aided sales at London-based Gem Diamonds.

The extremely rare and valuable yellow stones, many of which are mined from Gem's Ellendale mine in Australia, have become increasingly popular as the jewellery to be seen in.

Increasing demand means average prices of Ellendale yellow diamonds is $480 (£319) a carat compared with the overall average from the mine of $232 (£154).

Tiffany struck a deal with Gem to buy all of Ellendale's yellow diamonds, which will further add to the cachet of the stones.

Gem supplied Angelina Jolie, Jennifer Lopez and Beyoncé for jewellery at recent high-profile events, although it is not known from which producer Winslet's diamond came.

Gem made a profit last year while most bigger rivals struggled. Underlying pre-tax profits were $37.1 million (£24.67 million) compared with a loss of $367 million (£244 million) in 2008, when it was hit by a $338 million (£257.9 million) impairment charge.

Clifford Elphick, Gem's chief executive, said: "2009 was an extremely challenging year and saw us cut back on all non-core expenditure with the majority of development projects put on care and maintenance. We are currently reviewing growth possibilities."

He said he had high hopes for increased demand in new markets such as China and India which would add to the main markets of the US and Europe.