Different gemstones have different colors, glosses, etc. It is precisely due to their unique physical structure that gemstones have some special optical effects under light.
1.Asterism
Under the illumination of a point-light, the curved convex gemstone presents an optical phenomenon of four-, six-, or twelve-point lines, similar to the starlight in the night sky, which is called asterism. Common gemstones with asterism include star ruby, star sapphire, rose crystal etc.
2. Chatoyancy
Curved gemstones show bright bands of light on the surface of the gemstones when illuminated by light. When turning the gem, the light band moves with it, like the cat's eyes, and it is called chatoyancy. The chrysoberyl that has chatoyancy is called cymophane. Other common gemstones can exhibit an ‘eye’ including tourmaline, jadeite etc.
3. Discoloration effect
Gems show different colors under different light sources such as sunlight or sum lamp. This is called the gem's discoloration effect. It is called "emerald in the day, ruby in the night." The chrysoberyl with a discoloration effect is called a metamorphic stone. Other gemstones with color-changing effects include color-changing sapphire.
4.Play of Color
Under the illumination of white light, a phenomenon of multicolor transformation is displayed on the same gemstone at the same time. When turning a gemstone or light source, it can be seen that a variety of colors are constantly changing, sparkling and charming, and a rainbow-like colorful spectrum appears. The color change effect is more commonly seen in Opal.
5. Sheen
Moonstone is a microclimatic feldspar with lattice-like twin crystals. Two groups of twin crystal grains that are approximately perpendicular to each other scatter incident light. Dense scattered light is concentrated together and has a hazy halo like moonlight effect. Microclinic feldspar with moonlight effect is called moonstone.
6.Aventurescence
When a transparent to translucent gem contains many opaque tiny solid inclusions, it reflects and sparkles under the light, which is called aventurescence.
Common gemstones with aventurescence include sunstone, aventurine, etc..
7.Fluorescence effect
Luminous gemstones with fluorescence or phosphorescence. The most representative gemstone is fluorite, known as the "night pearl". Fluorite can emit tens of hours after being illuminated by fluorescent lamps. This light is relatively faint, invisible during the day, but bright at night. Fluorescence effect is one of the important basis for identifying natural gemstones.
8.Iridescence
There are two situations that are known as iridescence:
(1) When gemstones such as labradorite are rotated to a certain angle, the entire sample is illuminated, and it can show blue, green and gold, yellow, purple, red and other colors, which are called iridescence.
(2) The color of pearl is the color neutralized by body color, overtone, and iridescence. Pearl iridescence refers to the floating rainbow color formed on the surface of the pearl or under the surface, which is observed from the light reflected from the surface of the pearl. It is a special luster formed by the combined effect of the reflection and interference of light on the subsurface of the pearl.
9. Thin film interference effect
Some gemstone crystals have an extremely thin crack surface inside, and light interfere through the crack surface to make an optical effect of colorful light, which is called a thin film interference effect.
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