Jade: the material
The English term 'jade' is used to translate the Chinese word yu, which in fact refers to a number of minerals including nephrite, jadeite, serpentine and bowenite, while jade refers only to nephrite and jadeite. Chemically nephrite is a calcium magnesium silicate and is white in colour. However, the presence of copper, chromium and iron gives colours ranging from subtle grey-greens to brilliant yellows and reds. Jadeite, which was very rarely used in China before the eighteenth century, is a silicate of sodium and magnesium and comes in a wider variety of colours than nephrite.
Nephrite is found within metamorphic rocks in mountains. As the rocks weather, the boulders of nephrite break off and are washed down to the foot of the mountain, from where they are retrieved. From the Han period (206 BC - AD 220) jade was obtained from the oasis region of Khotan on the Silk Route. The oasis lies about 5000 miles from the areas where jade was first worked in the Hongshan (in Inner Mongolia) and the Liangzhu cultures (near Shanghai) about 3000 years before. It is likely that sources were known that were much nearer to those centres in the early periods and were subsequently exhausted.
On loan from the Natural History Museum (nephrite);On loan from a private collection (jadeite)