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Gemstones are defined by their colors, a truly remarkable feature that determines both their beauty and value. Have you ever wondered what natural phenomenon leads to their natural color? Why does a blue sapphire appear blue and an emerald green? The science of gemstone colors lies within their chemical composition and their interaction with light of different wavelengths.
Understanding this science of gemstone hues is crucial when purchasing them. Of course, not everybody is a gemologist. You just can't analyse a gem under the microscope. But having basic knowledge helps you avoid fakes, identify treatments, and appreciate
the natural uniqueness of a stone. This blog serves as a quick guide.
Gemstones are composed of minerals, which in turn are made up of atoms. The arrangement of atoms in a crystal lattice forms a three-dimensional structure, providing the basis for a natural gemstone. The presence of elements inside these determines the color of the stone. The number of elements can vary; for instance, diamonds are made of pure carbon.
Sapphire's mineral, corundum, is composed of elements aluminum and oxygen.
Transition metals: These elements play an important role in determining gemstone color. Chromium, iron, titanium, vanadium, and copper are often responsible for the vivid hues of gemstones. Read More: What is the Chemical Composition of Ruby and Sapphire?
The emerald stone is green due to the presence of trace elements, primarily chromium. The more intense the chromium in the stone, the more fascinating the color.
Color centers: Color centers in gemstones are defects or imperfections in the crystal lattice. When light of a specific wavelength falls on it, the phenomenon of absorption and scattering occurs, giving the stone its color. For instance, in the yellow sapphire stone , the color is due to the presence of the trace element iron.
If the gemstone has a pale color, to give it a brighter hue, color centers are artificially induced. This intensifies the gem color. These color centers fade over time; therefore, it is always recommended to buy natural untreated yellow sapphire. These are considered more stable and valuable. Learn More: Yellow Sapphire Gemstone Grading Factors
The principle of light interaction governs gemstone hues. According to the science of gemstones, the visual color is due to the phenomenon of reflection, refraction, absorption, and dispersion.
Absorption: It is the phenomenon where light penetrates the gemstone and specific wavelengths are absorbed by its chemical structure. A range of specific wavelengths, in the form of colors, pass through the gemstones. So why sapphire appears blue to you is due to the absorption phenomenon. Trace elements like iron and titanium absorb specific light frequencies, producing a vivid blue color.
Reflection: The process where light strikes and bounces back is referred to as reflection. Their refractive index determines the brilliance and sparkle in gemstones. The higher the refractive index, the slower light slows down and bends more. This creates a change in light’s direction, resulting in higher brilliance. A faceted diamond reflects more brilliance compared to a poorly cut diamond. Learn More: Brilliance in Gemstones: An All-Inclusive Guide
Besides the two phenomena mentioned above, which are responsible for gemstone hues, other factors need to be considered.
Pleochroism: When a gemstone is observed from different angles, it appears to have different shades. Light is absorbed at different crystal axes or atomic arrangements. This results in producing a different color in each direction. Tanzanite stone is the best example of pleochroism in gemstones. When you turn it around, you will see different hues, such as blue, violet, and burgundy. Read Further: The Science of Pleochroism in Gemstones
Color Changing Effect: A color change in gemstones refers to stones that exhibit different colors in both daylight and incandescent light. The classic example is the alexandrite stone , which appears greenish in daylight and brownish-purple-red under lamp light. Read More: Alexandrite: How the Color Change Phenomenon Impact Stone Price?
Cut and Clarity: A precise cut enhances light reflection and refraction, intensifying the depth and vibrancy of gemstone hues. Clarity means how clean the stone is. The higher the clarity, the more light passes through the stone, resulting in a brighter color. A poorly cut and included ruby stone obstructs light, making the gem appear dull.
Every gemstone carries a distinct feature, especially the hue. What brings this is the science, making it the exclusive example of the art of nature. While purchasing a gemstone, hues or colors matter a lot. This is one of the critical factors in determining its price.
Therefore, a pale blue sapphire with high inclusions is priced lower, while a vivid sapphire is highly valued. If you are looking for a wide variety of gemstone shades, explore our collection at Navratan.
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