For corundum with starlight effect, ruby and sapphire are more valuable. The reason of starlight effect is that there are some needle-like impurities (rutile needles) in gemstones, which are distributed in a certain position of the stone in a neat and parallel way, forming channels. When this part is polished into a convex surface, the reflection phenomenon will appear as a light band. The starlight effect of corundum usually presents six starlight bands with 12 starlight bands in the middle. The light bands intersect at an angle of 60 degrees, and the clearest starlight usually appears in the gray-blue translucent sapphire. The color saturation of this corundum itself is usually low, but because our attention is on the clarity of starlight lines, the requirements for its own color are not so harsh. For example, the star stone of pink treasure is sometimes called the star stone of red treasure. The starlight effect is to follow the movement of light. With relatively concentrated light, such as the light emitted by a flashlight, it is easy to see the stars. Of course, it is best to see the starlight clearly in ordinary light. The straighter and brighter the line, the higher the value.

It should be noted that the common black starlight stone in the market generally refers to the starlight black treasure produced in Thailand, and the starlight is not long and not so obvious. It is the most characteristic of black gemstones and the cheapest and easiest to own among corundum starlight stones.