There are a lot of imitation jade in the market. They look like the real jade mineral but are actually synthetically manufactured. Some are composite material and have the same Refractive Index as Jadeite Jade (RI 1.66, Read here) as powdered mineral of JJ are added on in the production.
Jadeite Jade is cool to the touch while plastic warms up easily. If you have a piece of green ‘jade’ and am not sure of whether it is a stone or a plastic, rub it in between your thumb and forefinger. Believe me, not many people do that. Rubbing a small jade piece to determine whether it is jade mineral is really unorthodox but this is what we called the negation test. You have to use all your 5 senses when it comes to identification, plus your instinct as well, when you have paid some money to learn the ropes and you have bought some duds.
Certain tests only aid in the identification and is not affirmative. That is, you cannot be positive in the identification that your specimen is a Jadeite Jade, but you can rule out totally that the specimen is ‘positively’ not Jadeite Jade. Contrast this with my earlier post on “Gimmick Test Is Not Conclusive” (Read here)
This type of instinctive testing is valuable in the field when you are a buyer, armed with only a loupe and every seller tells you that they sell the natural stone. (Read here)
Jadeite Jade is a crystalline mineral. It conducts heat away faster than plastic material. If it warms up easily then chances are it is likely to be some other material than Jadeite Jade.
If you have a small cabochon place it in your cheek for this area is more heat sensitive than your thumb and forefinger. If it still feels cool after a while the piece is probably not plastic. Caution: do not jump to conclusion that this is jadeite jade. Remember this is only a negation test.
Other things to consider are the size and the thickness of the specimen. As you go along you will be wiser when you are armed with some basics and fundamentals. (Read here for Fundamentals).
The above negation test also works for other gemstones as well to separate between natural minerals and plastics.