Color is a result of the way gemstones absorb light. The human can only perceive wavelengths between 380 and 750 nm. These visible colors are red, orange, yellow, green, blue, indigo and purple.
If all the different wavelengths of light pass through a gemstone, it will appear colorless. On the other hand, if the gem material absorbs all light, it will appear to be black. But if a stone absorbs all wavelengths except those in the red part of the spectrum, the gem will appear red. These gems that absorb certain wavelengths are idiochromatic. an example of an idiochromatic gemstone is Peridot.
Idiochromatic gemstones are rare. Most of the gemstone acquire color by impurities or trace or elements in their crystal structure. They are allochromatic. A Corundum is a colorless gemstone, but it becomes a ruby when there exist traces of chromium or it becomes a sapphire when there exist traces of titanium.
The third way to acquire color is by human intervention. It is used to change the chemical state of impurity in order to deepen or lighten the color.
red – ruby/garnet
pink – tourmaline/spinel
blue – sapphire
green – emerald
Benc Tan 