Donghai County (simplified Chinese: 东海县; traditional Chinese: 東海縣; pinyin: Dōnghǎi Xiàn; lit. 'east sea') is under the administration of Lianyungang, Jiangsu province, China. It borders the prefecture-level cities of Linyi (Shandong) to the north and Xuzhou to the west. The county has 300 million tons of quartz and 300,000 tons of rock crystal reserves, which is the highest in China, so it is nicknamed "the county of rock crystal".