This describes the degree to which light can pass through the stone, so that objects are visible through it. Transparency and clarity are interlinked -inclusions can block the passage of light.
The following terms are used to describe gemstone transparency:
Transparent -objects seen through the stone look clear and distinct. That is, it allows light to pass through it without diffusing (scattering) the light. Such stones usually have excellent brilliance, even if they might have some minor inclusions common to that particular gem type. The word "Crystal" is also often used to describe such stones.
Semi-transparent -objects look slightly hazy or blurry through the stone.
Translucent -objects are vague and hard to see through the stone. It allows light to pass through it, but the light is somewhat diffused.
Semi-translucent or semi-opaque -a small fraction of light passes through the stone, mainly around the edges.
Opaque -virtually no light passes through the stone.
Sometimes, "near transparent" is used as a category between transparent and semi-transparent, and the most transparent specimens of jade and opal, and many high-quality emeralds and rubies can fit into this category.
Often times, jade dealers use "translucency" instead of "transparency" to describe jade.
Other terms often used to describe gemstone transparency are:
Crystal (highly transparent)
Sleepy (low transparency)