Explain why gemstones have such vivid colors.

In short (click here for detailed version)

The bright colors of gemstones are generally due to the presence of impurities or chemical elements in their crystalline structure, which absorb or scatter certain wavelengths of light and thus give these characteristic colors.

Explain why gemstones have such vivid colors.
In detail, for those interested!

Interaction of light with the crystalline structure

When light passes through a gemstone, it encounters regularly arranged internal structures that are very precisely organized: the famous crystals. This organization acts somewhat like a tiny network that alters the path of light rays. Depending on how the crystal structure is organized, certain wavelengths will be absorbed while others continue on their path or reflect towards the eye. This natural selection performed by the crystal results in the bright color we observe. The more ordered and precise the internal structure of the crystal is, the more spectacular and intense the play of light is, giving the gem its famous colored sparkle.

Influence of trace elements and chemical impurities

Tiny amounts of foreign chemical elements in gemstones significantly alter their colors. Just a little bit of chrome is enough to make a red corundum (ruby) or a green emerald, while a few atoms of iron produce the blue of sapphire or the yellow of citrine. These chemical impurities, also known as trace elements, absorb specific colors from the full spectrum of white light, and it is this selective absorption that gives each gem its intense and unique color. Without these tiny chemical intruders, many gemstones would be dull or even completely transparent.

Role of selective absorption of wavelengths

When white light hits a gemstone, certain wavelengths are absorbed while others are reflected or pass through the crystal. This selective filtering comes directly from its chemical composition and internal structure. The absorbed wavelengths then disappear from the light spectrum, while those that emerge give the gem its characteristic color. An emerald, for example, primarily absorbs reds and blues, allowing mainly the green you perceive to pass through. Each gem acts like a kind of natural selective filter capable of providing a vivid and unique color based on its composition. This specific absorption is the reason behind the vibrant and captivating colors of gemstones.

Particular optical effects: fluorescence and phosphorescence

Some gemstones have a surprising ability: they absorb light and then re-emit it in the form of luminescence. This is fluorescence, an ultra-fast reaction that stops immediately as soon as the stone is no longer exposed to light. Other stones, after being illuminated, continue to glow subtly even when plunged into darkness: this is phosphorescence, a slower phenomenon where the absorbed light energy is gradually released. These optical effects often arise from small impurities and defects in the crystal lattice, which act as energy traps. This is what gives the stones a magical quality: under black light or in total darkness, they suddenly shift from an ordinary color to intense and vivid shades that are completely surprising.

Impact of pleochroism on color intensity

Some gemstones change in intensity and even color depending on their orientation: this is called pleochroism. This phenomenon occurs when light interacts differently depending on the angles at which it passes through the crystals. The classic example? Tanzanite, which appears blue from one angle but shifts to purple or reddish-purple when you turn it. The intensity and visual richness of stones like cordierite or alexandrite arise precisely from this subtle interplay of angles and light. It is this special effect that can give gemstones so much charm and visual depth.

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Frequently Asked Questions (FAQ)

1

Does the color of a gemstone affect its market value?

Sure! Here’s the translation: "Yes. Generally, the brighter, rarer, and more sought-after a color is, the more precious the stone becomes. Color is one of the fundamental criteria for determining the value of a gemstone, in addition to purity, weight, and cut."

2

Do gemstones lose their color over time?

In most cases, no, but they can slightly alter under certain conditions. Some gemstones may change or slightly lose their color intensity when exposed to intense light, excessive heat, or certain chemical treatments.

3

What is the phenomenon of pleochroism, and do all gemstones exhibit it?

Pleochroism is the optical phenomenon observed in certain stones where different colors appear depending on the angle of view. Not all gemstones exhibit this phenomenon. It primarily depends on the crystal structure of the stone and how it interacts with light.

4

How can we distinguish a natural gemstone from a treated or synthetic one?

Natural gemstones generally exhibit characteristic inclusions that are visible under a microscope or with a loupe. The use of specialized equipment, such as spectroscopy or infrared analysis, often enables gemologists to distinguish natural stones from those that have been treated or synthesized in a laboratory.

5

Why can two gemstones of the same type have different colors?

The variations in colors within the same family of gemstones often stem from slight differences in chemical impurities, the presence of trace elements, or minor structural alterations in their crystal lattice.

Natural Sciences

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