Fyodor Andreev leaves Alrosa, based in the Sakha Republic.
Gem weights in at 27.85 carats, and may become the most expensive polished diamond in the company's history.
The Siberian producer - owned mainly by the Russian state and the Sakha government - hopes to shine on the international market.
The world's top diamond producer is on course for a $10 billion valuation, say analysts.
Current president of Sakha-based company leaves after 'difficult' relationship with senior officials in Moscow.
A 44 per cent decline in diamond production was announced by Russian gem producer Alrosa.
Proceeds of a sale of a stake in Alrosa diamond giant will benefit local people, vows governor.
Giant gem goes on show as Siberian diamond company Alrosa issues a 16% stock float.
But there are questions over privatisation of mining giant Alrosa, the world's largest producer.