Jadeite is a mineral species established by A. Damour in 1863, differing markedly from nephrite in that its relation lies with the pyroxenes rather than with the amphiboles. It is an aluminium sodium silicate, NaAl(SiO3)2, related to spodumene. S. L. Penfield showed, by measurement, that jadeite is monoclinic. Its colour is commonly very pale, and white jadeite, which is the purest variety, is known as "camphor jade." In many cases the mineral shows bright patches of apple-green or emerald-green, due to the presence of chromium. Jadeite is much more fusible than nephrite, and is rather harder (6.5 to 7), but its most readily determined character is found in its higher specific gravity, which ranges from 3.20 to 3.41. Some jadeite seems to be a metamorphosed igneous rock. The Burmese jade, discovered by a Yunnan trader in the 13th century, is mostly jadeite. The quarries, described by Dr F. Noetling, are situated on the Uru river, about 120 m. from Mogaung, where the jadeite occurs in serpentine, and is partly extracted by fire-setting. It is also found as boulders in alluvium, and when these occur in a bed of laterite they acquire a red colour, which imparts to them peculiar value. According to Dr W. G. Bleeck, who visited the jade country of Upper Burma after Noetling, jadeite occurs at three localities in the Kachin Hills--Tawmaw, Hweka and Mamon. The jadeite is known as _chauk-sen_, and is sent either to China or to Mandalay, by way of Bhamo, whence Bhamo has come erroneously to be regarded as a locality for jade. Jadeite occurs in association with the nephrite of Turkestan, and possibly in some other Asiatic localities. In certain cases nephrite is formed by the alteration of jadeite, as shown by Professor J. P. Iddings. The Chinese _feits'ui_, sometimes called "imperial jade," is a beautiful green stone, which seems generally to be jadeite, but it is said that in some cases it may be chrysoprase. It is named from its resemblance in colour to the plumage of the kingfisher. The resonant character of jade has led to its occasional use as a musical stone.