LONDON, Nov 16 (Reuters) - A top shareholder in Glencore

GLEN.L , Abu Dhabi's Aabar Investments, has written off more $392 million of its $1 billion investment in the commodities trader, less than two years after taking part in its record listing.

Aabar, a unit of Abu Dhabi's state-owned International Petroleum Investment Co INPTV.UL , became the largest new shareholder in Glencore when the mining-to-trading giant went public in May 2011, investing $1 billion.

According to financial statements filed by IPIC on Thursday, Aabar, which owns 1.4 percent of Glencore, has recognised an impairment loss of $392 million. It gave no further details.

Glencore's shares are trading almost 40 percent below an IPO price of 530 pence, underperforming by more than 10 percent a mining sector that has been hit by worries over cooling demand - despite hopes its marketing arm would help weather stormier times for the commodities markets.

The writedown comes as Glencore, the world's largest diversified commodities trader, moves into the final stages of its long-awaited takeover of miner Xstrata XTA.L , in which it is already the largest shareholder.

Qatar, which has become the second-largest shareholder in Xstrata, said on Thursday it would vote in favour of the deal.

IPIC said in the same interim financial statement that it had booked a fair value loss of $660 million on its shares in Italian bank UniCredit CRDI.MI , though a gain of $51 million on its stake in automaker Daimler DAIGn.DE .

IPIC said its profit for the six months to the end of June totalled $818 million, down from $1.16 billion a year ago.

(Reporting by Clara Ferreira-Marques; Editing by Jon Hemming)

((clara.ferreira-marques@thomsonreuters.com)(+44 207 542 3214)(Reuters Messaging: clara.ferreira-marques.thomsonreuters.com@reuters.net))

Keywords: GLENCORE AABAR/