What is Jade?

'Jade', or Yu, as it is called in China, is strictly speaking a generic term for two different gems, nephrite and jadeite. The name is derived from the Spanish 'piedra de ijada', loin-stone, jade having been recognized by the Amerindians as a remedy for kidney ailments. Because of its beneficial effect on the kidneys, the stone was also known as 'lapis nephriticus'. That, indeed, is where the term 'nephrite' came from. Jadeite and nephrite are both regarded in China as 'zhen yu', 'genuine jade'. It was not until the beginning of the 19th century that mineralogists and gemologists started to differentiate between them, since they bear a considerable resemblance to each other in terms of their appearance, their hardness and the properties they exhibit when being processed. Both are tough, since they consist of dense, close-grained, matted aggregates, but they differ from one another in their chemical composition and colors. Nephrite ranges mainly from mid to dark green or grey-green, but it can also be white, yellowish or reddish. Rarer, and somewhat tougher, jadeite displays hues which include green, but also white or pink, and reds, blacks, browns and violets. In both minerals, the way the color is distributed varies a great deal. Only in the very finest jade is the color evenly distributed. Both nephrite and jadeite often have veins, blemishes and streaks running through them, though these may not always be regarded as flaws. On the contrary, some of these patterns are considered particularly valuable.

Jade can be categorized into two major groups:
1. Jadeite: Ying (hard) jade, more valuable.
2. Nephrite: Ruan (softer) jade, less durable.