Hainan, separated by the Qiongzhou Strait from the Leizhou Peninsula of Guangdong, is the largest island administered by the People's Republic of China and the 42nd largest in the world. The area of Hainan Island is similar to that of Belgium or slightly smaller than that of Taiwan. To the west of Hainan Island is the Gulf of Tonkin. Wuzhi Mountain is the highest mountain on the island at 1,840 m (6,040 ft).The northern half of Hainan is covered with the ancient Hainan Volcanic Field. Beneath the topsoil is volcanic rock while the topsoil itself contains small pieces of this vesicular rock.