|Varieties of Jade
Jade has been known and treasured for more than 7,000 years. In prehistoric times, jade was used in many parts of the world for arms and tools because of its exceptional toughness. For over 2,000 years, jade was part of the religious cult in China and mystic figures and other symbols were carved from it. In pre-Columbian Central America, jade was more highly valued than gold.
But only in 1863 was it discovered that jade is actually not a single mineral. What was traditionally called jade is in fact two separate and distinct minerals: jadeite and nephrite.
Nephrite is the more common form of jade. Nephrite ranges in color from mid to dark green or grey-green, but it can also be white, yellowish or reddish. Nephrite is slightly softer than jadeite; nephrite is 6-6.5 on the Mohs scale, while jadeite is 6.5-7. They have quite different chemical compositions as well: nephrite is a calcium magnesium iron silicate while jadeite is a sodium aluminum silicate. The two minerals also have different densities. Jadeite has a density of 3.30-3.38 while nephrite is less dense at 2.90-3.03.
The two varieties of jade even have different crystal structures. While jadeite's structure is an arrangement of grainy crystals, nephrite is made up of fibrous crystals that interlock in a matted texture. These densely packed and interwoven fibers are extremely resistant to fracturing. So while jadeite is the denser and harder jade, nephrite is actually the tougher of the two.
All of the traditional Chinese jade is nephrite, since there are large deposits of nephrite in China, but no jadeite. Jadeite first came to China from Burma in the 18th century. Before the introduction of jadeite, the Chinese tended to value translucent white nephrite. But the jadeite from Burma came in a wider range of colors, including green, lavender, yellow, black and white. The rarest and most valuable jadeite is the imperial jade, colored by traces of chromium. It has color and transparency rivaling fine emerald, though imperial jade is slightly more yellow in tone. In fact the revered Emerald Buddha in Wat Phra Keow in Bangkok is believed to be composed of fine jadeite, not emerald.
Jadeite deposits are principally found in upper Burma. Other deposits are found in Japan, Canada, Guatemala, Kazakhstan, Russia and California. Nephrite deposits are found in China, Burma, New Zealand, Australia, Brazil, Canada, Zimbabwe, Russia, Taiwan and Alaska.
- First Published: October-04-2008
- Last Updated: March-10-2011
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