Jade is the Mystical birthstone for March and is a cherished gift on the 12th, 30th and 35th wedding anniversary. Jade has long been considered the health, wealth and longevity stone, used for courage, wisdom, love, and harmony. Jade is a very protective stone and will keep its wearer out of harm's way.

Jade, which has a discreet but greasy luster and comes in many shades of green, as well as shades of white, grey, black, yellow, and orange and violet, has been used by humans for nearly 7000 years. The earliest known jade artifacts excavated from prehistoric sites are simple bead, button, and tubular shapes. In prehistoric times, jade was appreciated for its hardness, which made it ideal for making weapons and tools. The earliest Maoris of New Zealand carved weapons from native jade, a tradition that continues today.

As early as 3000 B.C. jade was known in China as 'yu' or the 'royal gem'. Throughout the history of the Chinese Empire jade has been regarded like gold and diamonds have been in the West. During the pre-Columbian period, the Mayas, Aztecs and Olmecs of Central America also prized jade more highly than gold. Today, jade is regarded as a symbol of the good, the beautiful and the precious. It embodies the Confucian virtues of wisdom, justice, compassion, modesty and courage. In ancient Egypt, jade was admired as the stone of love, inner peace, harmony and balance.

Jadeite or Nephrite
Jade, or “yu,” as it is called in China, is actually a generic term for two different types of metamorphic rock, “nephrite” and “jadeite”. The English words “jade” and "jadeite” are derived from the Spanish term “piedra de ijada” or "loin stone", because of its reputed efficacy in curing ailments of the loins and kidneys. Nephrite is derived from “lapis nephriticus”, the Latin version of the Spanish “piedra de ijada”.

Nephrite and Jadeite are both regarded in China as 'zhen yu', 'genuine jade'. It was not until the beginning of the 19th century that mineralogists and gemologists began to differentiate between these two stones. Nephrite and jadeite are very similar in appearance because they are both dense, close-grained, matted aggregates. They differ from one another in most other ways, including their chemical composition, their colors and their hardness; jadeite measures between 6.5 and 7.0 on the Mohs Scale of Hardness and Nephrite between 5.5 and 6.0.

Nephrite primarily ranges in color from mid to dark green, but can also be a creamy white with a yellow or red tone, know in China as “mutton fat” jade. Jadeite is rarer and shows more color variety. Also primarily green, jadeite can be white, pink, red, black, brown or violet. The way color is distributed in these stones varies a great deal. Both nephrite and jadeite often have veins, blemishes and streaks. These naturally occurring variations are not always regarded as flaws in fact many add value to the stone. Only the very finest jade is uniformly colored. Translucent emerald-green jadeite is the most prized variety, both today and historically.

Is Serpentine or Soocho Jade?
Serpentine, sometimes called “Soocho” jade is an attractive green stone that takes a nice polish and is suitable for carving. It is frequently used as a substitute for jade and is sometimes difficult to distinguish from jade. Though color and the greasy luster are shared by serpentine and jade, the two stones are chemically very different. Serpentine is a much softer stone and is usually olive green to yellow in color, in contrast to the emerald green of most true jade.

Soocho Jade (also spelled Souchow/Suzhou/Suchow/Soo Chow) is named after the Chinese city of Suzhou. Suzhou is at the lower end of the Yangtze River in the province of Jiangsu, China. Although the trade name for this beautiful gemstone is Soocho Jade, it is actually serpentine. The beautiful colors of this semi-precious stone are created via heat-treatment –heating the serpentine to different temperatures, results in permanent color change.

Sources:
http://www.gemstone.org/gem-by-gem/english/jade.html
http://www.galleries.com/minerals/silicate/jadeite/jadeite.htm