described it as an "enigmatic archaism of politely pleasant or poetic usage", and "one of the most elusive terms in Chinese mineralogy". Identifications of langgan comprise at least three categories: Blue-green langgan was first recorded circa 4th century BCE, Coral langgan from the 8th century, and Red langgan is from an uncertain date. Edward H. Schafer, an eminent scholar of Tang dynasty literature and history, discussed langgan in several books and articles. His proposed identifications gradually changed from Mediterranean red coral, to coral or a glass-like gem, to chrysoprase or demantoid, to coral or red spinel, and ultimately to malachite. Blue-green langgan Langgan was a qīng 青 "green; blue; greenish black" (see Blue–green distinction in language) gemstone of lustrous appearance mentioned in numerous classical texts. They listed it among historical imperial tribute products presented from the far western regions of China, and as the mineral-fruit of the legendary langgan trees of immortality on Mount Kunlun. Schafer's 1978 monograph on langgan sought to identify the treasured blue-green gemstone, if it ever had a unique identity, and concluded the most plausible identification is malachite, a bright green mineral that was anciently used as a copper ore and an ornamental stone. Two early Chinese mineralogical authorities identified langgan as malachite, commonly called kǒngquèshí 孔雀石 (lit. "peacock stone") or shílǜ 石綠 (lit. "stone green"). Comparing blue-green stones that were known in early East Asia, Schafer disqualified several conceivable identities; demantoid garnet and green tourmaline are rarely of gem quality, while neither apple-green chrysoprase nor light greenish-blue turquoise typically have dark hues. This leaves malachite, This handsome green carbonate of copper has important credentials. It is often found in copper mines, and is therefore regularly at the disposal of copper- and bronze-producing peoples. It has, in certain varieties, a lovely silky luster, caused by its fibrous structure. It is soft and easily cut. It takes a good polish. It was commonly made into beads both in the western and eastern worlds. Above all, even uncut malachite often has a nodular or botryoidal structure, like little clumps of bright green beads, one of the classical forms attributed to lang-kan. Sometimes, too, it is stalactitic, like little stone trees. Furthermore, archeology confirms that malachite was an important gemstone of pre-Han China. Inlays of malachite and turquoise decorated many early Chinese bronze weapons and ritual vessels. Tang sources continued to record blue-green langgan. Su Jing's 652 Xinxiu bencao