As explained in the previous post, the internal structure of Jadeite Jade comprises very minute granules of monoclinic microcrystalline crystals inter-locked against each other.
One of the factors in determining the quality of a jade piece is how compact would these microcrystalline crystals interlocked against each other. The more compact they are the finer would be the microcrystalline grains, the higher would be the quality of the jade piece. A very fine grain jade piece can also be subject to a high glossy polishing which will give its surface a shiny outlook.
One of the chief identifying characteristic of an unpolished jade would be the shiny reflections from individual crystals on the back of large or medium grain stones. Hence, during the auction of jade in Burma, jade dealers normally carried a bottle of water to splash on the surface of the open window of a rough jade piece. This would give you an idea on the texture of the jade grains and would indicate how the jade would look like after polishing.
Another identifying characteristic is that the surface of a jade piece is very dimpled even when the jade is polished. One can see the dimple surface even using a 10X loupe (read here on how to use a loupe). If the texture is of high quality the dimples would be more ‘shallow’ and further apart. Hence, jade is often waxed to hide these dimple surface.