The main diamond index held on to last week’s strong gains, opening a touch higher following a week of high trading volumes.%%The overall Polished Prices index, which covers all sizes between 0.3 carats and 3 carats, rose 0.4% to 129.2 points, an increase of 3.0% on the year so far, and 1.2% above the level of this time last year.%%Among the benchmark groupings, Mixed and Commercial quality 30 pointers, or 0.3 carats, were the strongest performers, adding 8.6% and 5.6% respectively.%%Commercial half carat diamonds opened almost unchanged, up 0.6%.%%However, all other benchmark categories were in negative territory.