Because the context speaks of the jewellery market.

As opposed to 'in tonnage terms' - http://www.lbma.org.uk/assets/PhilipKlapwijk.pdf or "in terms of its export earnings, employment generation, and growth" - https://www.dnb.co.in/IndianGemsandJewellerySector/Overview....

Sales of jewellery remained stable in terms of both volume with 67 million pieces and value at 3.8 billion Euros. They were down 1% in value for gold products and 10% higher for silver jewellery. The average price of the jewellery items sold also stabilised at 57 Euros, as had been the case in 2010 and 2009. Gold jewellery worth 2.5 billion Euros represents nearly 66% of the total value of all jewellery sales. Silver and gold- plated jewellery reached 0.8 billion Euros and represents 18.5% of sales. Fancy jewels account for just 13.3% of sales in value terms but 49.6% by volume. Turning to prices, 18 carat gold jewels sell at an average price of 250 Euros while those in 19 carat gold cost 102 Euros. Silver jewellery items sell for an average price of 36 Euros and gold-plated articles for 34 Euros. - http://www.wthejournal.com/en/news/view/french-watch-and-jew...