Light has an different effect on gem stones. This section will help you understand how light works to make gems different.
Transparent: The ability to see through an object to what is beyond. The most familiar transparent object we see every day is glass. There are many gem, rocks and stones that are transparent. I think of diamonds, crystal quarts, the beryls (emerald and aquamarine) when they are of excellent quality is transparent. My favorite test for transparency is to put the stone over a piece of paper with print on it and look through to the print. If you see the print below you have a transparent stone.
Translucent: The ability of an object to allow light to pass through it. Sometimes it is difficult to tell the difference between transparent and translucent. The paper and print test also applies here. If you can’t see the print hold the stone up to a strong light and look for light to pass though. When the light shines through the stone you have a translucent stone. Think of the chalcedony, a gem quality rhodocrosite and carnelian, they are all translucent.
Opaque: An opaque object will block light. You can do the above test above to determine whether a stone is opaque. When the stone fails the print and light test you can have a great confidence that stone is opaque. The two best know opaque stones are jaspers and turquoise, both fail the transparent and translucent test. An opaque stone will reflect light back but the light does not come through the stone.
Chatoyancy: The reflection of light in an opaque stone is due to the finishing of the stone or chatoyancy. Chatoyancy is a special optical effect usually seen in a opaque stones, known as a Cat’s Eye or some time called Tiger’s Eye. Rolling the gemstone between your fingers under a light source, look for a line of light. The line of light in the stone will move as you move the stone.