What are the Colors of Sapphires, and What Causes It?
Sapphires are nature's fun way of expressing colour. Among the most desired gemstones in the world, celebrated for their rich colours and stunning brilliance. While blue is the hue most commonly associated with sapphires, they can occur in an array of colours, each created by unique geological and chemical processes. From a geologist's view, let's dive into the science behind sapphire colours and what determines their diverse spectrum.
The Chemistry Behind Sapphires
Sapphires are a variety of the mineral corundum, which is composed primarily of aluminium oxide (Al₂O₃). Pure corundum is colourless. The diverse hues of sapphires are created from traces of elements incorporated into the crystal lattice during its formation. These trace elements, also known as chromophores, absorb and reflect specific wavelengths of light, giving the gemstone its distinctive color.
Blue Sapphires
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Cause: The iconic blue color of sapphires is primarily due to the presence of iron (Fe) and titanium (Ti) minerals. When these two elements substitute for aluminium in the corundum lattice, they create a phenomenon known as charge transfer, which absorbs specific wavelengths of light and imparts the blue hue.
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Shade Variations: Higher concentrations of iron and titanium result in deeper blue tones, while lower concentrations lead to lighter blues. The presence of other elements or variations in the stone’s internal structure can also influence the intensity of the color.
Pink Sapphires
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Cause: Pink sapphires owe their color to trace amounts of chromium (Cr). Chromium absorbs green and blue light, allowing red and pink hues to dominate the gemstone.
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Shade Variations: The concentration of chromium determines the intensity of the pink color. Higher chromium levels can lead to a transition from pink to red, creating a ruby (another variety of corundum).
Yellow and Orange Sapphires
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Cause: Yellow sapphires are colored by iron minerals, which absorb blue light, leaving a yellow appearance. Orange sapphires, on the other hand, often result from a combination of iron and chromium or iron and vanadium. Ceylon yellow sapphires can also be coloured by a phenomenon known as colour centers. The variations are endless with sapphire colors.
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Shade Variations: The specific combination and concentration of these elements determine whether the stone appears more yellow, golden, or orange. Gemmologists determine the grade of the stone by inspecting these elements.
Green Sapphires
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Cause: Green sapphires are the result of a type of iron impurities within the crystal lattice. Unlike the iron in yellow sapphires, the absorption spectrum of green sapphires is broader, leading to the perception of a green hue.
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Shade Variations: The green may vary from dark to pale to olive, depending on the iron content and the gemstone’s structural properties.
Purple and Violet Sapphires
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Cause: These hues are typically caused by the presence of chromium and vanadium (V) within the crystal structure. Vanadium absorbs yellow light, producing purple and violet shades.
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Shade Variations: Variations in vanadium and or chromium concentration influence whether the sapphire appears more violet or purplish.
Padparadscha Sapphires
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Cause: One of the rarest and most sought-after sapphire varieties, padparadscha sapphires exhibit a delicate pink-orange color. This unique hue results from a balanced combination of chromium and iron impurities.
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Shade Variations: The exact blend of pink and orange can vary, with premium padparadscha sapphires showcasing a perfect equilibrium of both tones.
White Sapphires
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Cause: White sapphires, also known as colorless sapphires, are free of significant chromophore impurities. They lack the trace elements needed to impart color, leaving them transparent or slightly cloudy.
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Applications: White sapphires are often used as a diamond alternative in jewelry due to their brilliance and durability.
Color Zoning and Saturation
In many sapphires, the distribution of color within the gemstone is not uniform. This phenomenon, known as color zoning, occurs due to fluctuations in trace element concentrations during crystal growth. Skilled gem cutters often orient these zones to maximize the stone's visual appeal.
Additionally, the saturation of a sapphire’s color—its intensity and depth—can greatly affect its value. Rich, vivid colors are generally more desirable than pale or overly dark hues.
Popular Sapphire Colours Used in Jewellery
Sapphires are known for their stunning spectrum of colours, and durability, and offer so much for personalisation. While blue sapphires are the most iconic due to the spotlight of British royalty, this precious gemstone is available in a range of hues, each with its own unique allure and rarity.
The Best Colours of Sapphires
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Rich, velvety royal blue sapphires are the most sought-after and timeless choice.
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Known for their deep saturation and even color, these sapphires exude elegance and sophistication.
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Often sourced from Sri Lanka or Kashmir, royal blue sapphires are a classic choice for engagement rings.
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A lighter, softer blue with a delicate, powdery hue often with a mix of violet tone.
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These sapphires are prized for their romantic and subtle appeal, ideal for those seeking understated luxury.
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Feminine and vibrant, pink sapphires range from soft pastel shades to vivid magenta.
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A popular choice for modern, unconventional engagement rings.
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A unique blend of blue and green tones, teal sapphires are perfect for those seeking a contemporary yet earthy gemstone.
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Their distinctive colouring makes them a favourite among couples looking for something rare and memorable.
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Radiant and cheerful, yellow sapphires range from pale sunshine to rich golden hues.
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They symbolise prosperity and optimism, making them a meaningful choice.
Choose your favourite color at Deliqa Gems! Email to design remotely or book a one-on-one in-person or remote appointment with Sasha to get a personalised experience looking at the vast selection of natural gemstones in inventory.