JERUSALEM, July 14 (Reuters) - Israel's net polished diamond exports reached $3.6 billion in the first half of 2014, up 6 percent from a year earlier, the Economy Ministry said.     Diamond exports comprise about 20 percent of Israel's total exports.     Israel's net imports of polished diamonds rose 3.2 percent to $2.2 billion in the January-June period.     Net rough diamond exports grew 6 percent to $1.8 billion, while rough diamond imports edged up 0.9 percent to $2.1 billion, the ministry said on Monday.     The United States remained Israel's largest export market for polished diamonds in the first half, accounting for 45 percent of gross exports, followed by Hong Kong, Switzerland and Belgium.     The Israel Diamond Institute (IDI) said the rise in exports  came despite tough economic conditions in major markets.     "We are optimistic that there will be further growth during the second half of the year," IDI Chairman Moti Ganz said.      (Reporting by Steven Scheer)  ((steven.scheer@thomsonreuters.com)(+972 2 632 2210)(Reuters Messaging: steven.scheer.thomsonreuters.com@reuters.net))  Keywords: ISRAEL DIAMONDS/EXPORTS