There are two types of  jade - jadeite and nephrite. The Chinese refer to jade as 'yu' meaning 'heavenly' or 'imperial'.  

Jadeite is the rarer of the two types of jade therefore more precious.

Nephrite is more common than jadeite. They can be found in China, Taiwan, etc.
The main source of jadeite is Myanmar (Burma) also the only source of imperial jadeite. 

However, imperial jade is not the only sought-after form of antique jade. Collectors also prize fine, white nephrite carvings for their translucent surface. Some jade contains dark russet inclusions, which early jade carvers would often work into the design of their pieces. Beautiful inclusions may also increase the value of a piece of jade.

Jade colours occur in green, white, orange, yellow, lavender, grey and black. 

The Chinese jade industry classifies jadeite by amount of enhancement received.
Grade A is not dyed nor impregnated. Grade B jadeite may have been impregnated and bleached but not dyed. Grade C jadeite is dyed and impregnated and Grade D jadeite is not real