Gaborone: Botswana, the world’s biggest diamond producer, cut its 2015 economic-growth forecast by almost half because of an expected decline in demand for the precious stones. The southern African nation now forecasts expansion at 2.6%, the Finance Ministry said in a 2016-17 budget document. That compares with a projection of 4.9% announced by the government in February.

“The downside risk to the projections continues to be the country’s high dependence on diamonds, whose demand and prices are subject to global fluctuations,” the ministry said. Diamonds are “the vast majority of their revenue and also the government’s finances,” Hanns Spangenberg, an analyst at NKC African Economics in Paarl outside Cape Town, said. “It’s definitely worrisome that they are still that dependent on the diamond industry, but it’s understandable that they cut the growth forecast.”

Diamonds mined by Debswana Diamond Co. Ltd., a government joint venture with Anglo American Plc’s De Beers unit, have helped transform Botswana from a poor, cattle-ranching society into the ranks of upper-middle income nations. The precious stones account for more than 70 percent of Botswana’s export revenue.