Jade = 2 types of stones: Jadeite and Nephrite.
Gemstone quality stones are Jadeites from Myanmar. Other "jades" from elsewhere is not really kept as precious jewellery.
4 types: A,B,C and B+C as follows:
A = au naturel - natural jadeite without any artificial treatment. Does not change with passage of time, will keep forever.
B = bleached with acid treatment and impregnated with resin. Will yellow gradually over 3-5 years and surface colour will fade.
C = Colored, treated and added with new pigment substances. [aka Dyed] colour will fade gradually.
B+C = bleached + colored.
A = au naturel - natural jadeite without any artificial treatment. Does not change with passage of time, will keep forever.
B = bleached with acid treatment and impregnated with resin. Will yellow gradually over 3-5 years and surface colour will fade.
C = Colored, treated and added with new pigment substances. [aka Dyed] colour will fade gradually.
B+C = bleached + colored.
Basically only buy Type A stones if thinking of keeping as heirloom. When Jade is modified/ impregnated with resin, resonance decreases and sounding the jade will produce a lowered tone, hence a clear resonating high pitch tone is good.
Colours of Jades include: Red, Yellow, Green, Lavender, Black and White. Most favoured are "Emerald Green" and "Apple Green".
Other things to consider: Clarity, Transparency [whole list of other things not that important/ is likely to be obvious].
Reference: lihongjade.com
