(IDEX Online) - The biggest diamond ever auctioned in Australia has sold for a record USD $870,000.The square emerald-cut diamond weighing 25.02 carats (pictured) went to an absentee bidder at the Leonard Joel Important Jewels auction in Sydney yesterday.It just about broke the million dollar (AUD) barrier. The hammer price was AUD $900,000, but the buyer's premium and GST (goods and services tax) pushed the total tag to AUD $1.125m. The hammer estimate for the gem, set in a platinum ring, was AUD $990,000 to AUD $1.2m.The previous record for a diamond sold at auction was AUD $575,000 (including buyer's premium and GST) - set by the same auction house for a 17.34 carat diamond ring sold last August.Yesterday's sale, with 234 lots, was described as the highest-grossing jewelry auction in Australia. It fetched a total of AUD $4.275m with buyers' costs, well below the low estimate of AUD $6.035m. Sixty-three per cent of lots were sold.