Kunlun Mountain. Texts from the turbulent Six Dynasties period (220-589) and Sui dynasty (581-618) used langgan gemstone as a literary metaphor, and an ingredient in alchemical elixirs of immortality, many of which were poisonous. During the Tang dynasty (618-907), langgan was reinterpreted as a type of coral. Several early texts (including the Shujing, Guanzi, and Erya below) recorded langgan in context with the obscure gemstone(s) qiúlín 璆琳. In Classical Chinese syntax, 璆琳 can be parsed as two qiu and lin types of jade or as one qiulin type. A recent dictionary of Classical Chinese says qiú 璆 "fine jade, jade lithophone" is cognate with qiú 球 "precious gem, fine jade; jade chime or lithophone" (which later came to mean "ball; sphere"), and lín 琳 "blue-gem; sapphire". In what may be the earliest record, the c. 5th-3rd centuries BCE Yu Gong "Tribute of Yu the Great" chapter of the Shujing "Classic of Documents" says the tributary products from Yong Province (located in the Wei River plain, one of the ancient Nine Provinces) included qiulin and langgan jade-like gemstones: "Its articles of tribute were the k'ew and lin gem-stones, and the lang-kan precious stones". Legge quotes Kong Anguo's commentary that langgan is "a stone, but like a pearl", and suggests it was possibly lazulite or lapis lazuli, which Laufer calls "purely conjectural". The c. 4th-3rd centuries BCE Guanzi encyclopedic text, named for and attributed to the 7th century BCE philosopher Guan Zhong, who served as Prime Minister to Duke Huan of Qi (r. 685-643 BCE), uses bi 璧 "a flat jade disc with a hole in the center", qiulin 璆琳 "lapis lazuli", and langgan 琅玕 as examples of how establishing diverse local commodities as fiat currencies will encourage foreign economic cooperation. When Duke Huan asks Guanzi about how to politically control the "Four Yi" (meaning "all foreigners" on China's borders), he replies: Since the Yuzhi [i.e., Yuezhi/Kushans in Central Asia] have not paid court, I request our use of white jade discs [白璧] as money. Since those in the Kunlun desert (modern-day Xinjiang and Tibet) have not paid court, I request our use of lapis lazuli and langgan gems as money. … Since a white jade held tight unseen against one's chest or under one's armpit will be used as a thousand pieces of gold, we can obtain the Yuezhi eight thousand li away and make them pay court. Since a lapis