Jade is actually two different minerals. One is nephrite jade(called soft Jade in China), a member of the amphibole family. The other is jadeite (called hard jade in China), one pyroxene mineral. Chinese ancient jade is nephrite jade. After about 1780, however, jadeite from Burma was imported in abundance into China and became one of the most widely used jade there.Jade is highly praised by the Chinese because it represents many sentiments in the Chinese people's eye.you can learn more by read Chinese Jade Culture.
Now that jade is one precious gem then How does one tell nephrite from jadeite?
Both types of jade are harder than a knife blade, fine-grained, translucent and colored in many shades of green, tan and brown. In a few cases, color can be a help. Very pale to nearly white jade is almost always nephrite. More boldly colored jade such as vivid malachite green, purple, blue or bright red is almost always jadeite. The colors are due to trace element impurities, such as iron, vanadium or manganese.
Some useful tests help distinguish jadeite from nephrite. A streak plate has a hardness of 6.5. Jadeite is harder than a streak plate, while nephrite is softer. Nephrite is less dense (3.0 grams/cc) compared to jadeite (3.3 grams/cc). Thus jadeite will sink in liquid methyl iodide, while nephrite will float. Jadeite will fuse relatively easily when hit with a blow torch flame, while nephrite will fuse only with great difficulty. This is obviously not a test to do on an antique! There are also subtle differences in appearance. Jadeite is glassier compared to a more waxy luster for nephrite. Nephrite is also tougher to break, even though it is softer on the Mohs' scale. This toughness is due to nephrite's internal structure which is made of many microscopic interlocking fibers put together like felt.
Jadeite and nephrite are both metamorphic minerals. Nephrite often forms in metamorphosed fragments of the crust and upper mantle faulted up when ocean crust and continental crust collide during mountain building. Jadeite forms when these rocks are pushed deep down subduction zones and experience low temperature but very high pressure. Only large scale faulting will bring jadeite-bearing rocks back to the surface. The best place to find such large vertical movements is in young mountain belts, like those forming in the Circum-Pacific and Himalayan zones. Thus, cultures of the Pacific Rim were those blessed with these remarkable gemstones.

Difficult to impossible to distinguish nephrite jade from jadeite jade by visual inspection.  Specific gravity determination is the most reliable of simple I.D. methods for distinguishing the two. Great variety of materials offered as imitations, e.g. talc (soapstone), serpentine, amazonite, dyed chalcedony, and others. All can have colors remarkably similar to jade, but properties above, particularly S.G., can be used to distinguish. Dyed jade can be most easily distinguished from undyed jade by examination with a Chelsea filter; undyed jadeite will not show the red color of dyed jadeite or nephrite when looked at through the filter.