10 Fascinating Stones That Change Color: A Deep Dive
Imagine holding a gem in your hand that transforms from a vibrant green under sunlight to a deep, passionate red under incandescent light. Welcome to the enthralling world of the top 10 stones that change color, natural wonders that captivate both gemologists and jewelry enthusiasts alike.
Explanation of Color Changing Phenomenon
Stones that change color demonstrate a fascinating phenomenon. The color transformation primarily depends on two factors: the type of light they are exposed to, and, for some, the temperature at which they exist. For instance, the same stone can project different colors under sunlight or fluorescent light. Furthermore, certain stones change their color based on temperature shifts – a cool trait known as thermochromism.
10 Stones That Change Color
1. Alexandrite
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Alexandrite is an exceptional variety of the mineral chrysoberyl. Its most striking feature is its ability to change color from green in daylight to purplish-red in incandescent light, which led to the phrase “emerald by day, ruby by night.” This change is caused by the unusual way the mineral absorbs light, which is a consequence of its unique chemical composition containing elements like chromium, iron, and titanium.
Alexandrite’s rarity adds to its allure. Originating in Russia’s Ural Mountains, it’s now also found in Sri Lanka, East Africa, and Brazil, though fine specimens remain scarce.
Value and Rarity: One of the most coveted and expensive gemstones due to its rare color-change ability and scarcity. High-quality Alexandrite with a pronounced color change can command prices higher than diamonds.
Identification: Genuine Alexandrite exhibits a dramatic color change from green in daylight to red in incandescent light. This can be tested under a gemological light source. More advanced tests like spectroscopy and microscopy, where the gem’s inclusions are examined, are necessary for a comprehensive identification.
2. Garnet (color-change variety)
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Although Garnet is commonly associated with a deep red color, it’s actually a group of minerals that can be found in a rainbow of colors. The color-change variety, typically found in Madagascar, exhibits a fascinating transformation.
In daylight, it appears to be greenish, brownish, or grayish. However, under incandescent or candlelight, it transforms into a deep, vibrant pink or red. This remarkable shift is attributed to the presence of trace elements like chromium and vanadium and how they interact with different light sources.
Value and Rarity: This variety is quite rare and lesser-known than its traditional red counterpart, but it’s highly valued by collectors and gem enthusiasts. Its value is determined by the strength of the color change, the size, and the overall quality of the stone.
Identification: This garnet’s unique color shift can be confirmed by observing the stone under different light sources. Detailed gemological testing, such as refractive index and specific gravity measurements, can be utilized for further authentication.
3. Sapphire (color-change variety)
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Known for their vibrant blues, Sapphires also have a lesser-known, color-changing variant. These extraordinary gemstones owe their color-change ability to the presence of trace amounts of vanadium in their crystal structure.
Under natural light, they exhibit shades of blue, but under artificial or incandescent light, they transform into lovely violet or purple hues. While traditionally associated with Myanmar and Kashmir, color-changing sapphires can also be found in Sri Lanka and Tanzania.
Value and Rarity: Quite rare and usually fetch higher prices than regular sapphires. Their value largely depends on the stone’s color, size, clarity, and the strength of the color change.
Identification: These sapphires change color depending on the light source, often switching between blue and purple. Gemologists use tools such as refractometers and spectrometers to test their refractive index and inspect their inclusions.
4. Diaspore
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Discovered in the early 1800s, Diaspore has only recently become popular in the gemstone market. Originating in the Anatolian Mountains of Turkey, it exhibits a captivating color change from kiwi-like green in daylight to champagne or pink under different lighting conditions.
This color change is due to a process called ‘intervalence charge transfer,’ which involves light absorption by the stone’s iron ions. Diaspore’s color variation, combined with its excellent hardness and cleavage, makes it an exciting addition to any gemstone collection.
Value and Rarity: While Diaspore is not as well-known as other color-changing gems, it has gained recognition for its unique color shift. High-quality Diaspore that displays a clear color change can be quite valuable. However, since it’s a relatively new gem on the market, its price can vary significantly.
Identification: Diaspore exhibits a color change from greenish in daylight to pinkish under incandescent light. This change can be detected under a gemological light source. The stone’s refractive index, specific gravity, and pleochroic colors can be measured for further verification.
5. Opal
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One of the world’s most beautiful gemstones, Opal, is cherished for its play-of-color phenomenon, an interplay of multiple colors that flash and change as the stone is moved. Rather than a change of color with light or angle, opals show a unique spectral delight, which is due to the diffraction of light passing through tiny silica spheres within the stone. Australia is the primary source of opals, with Ethiopian opals gaining popularity recently.
Value and Rarity: The value of opals is mainly determined by their play-of-color, color range, pattern, and brightness. While not traditionally considered a color-change stone, the incredible color variation in opals can command high prices, especially for high-quality Australian opals.
Identification: Opals are identified by their play-of-color, which can be viewed from different angles. Gemologists can also inspect the stone’s body color, pattern, and transparency. A microscope can be used to examine the stone’s structure and any inclusions.
6. Labradorite
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Known for its arresting optical phenomenon called labradorescence, Labradorite is a feldspar mineral that showcases an iridescent play of colors. The most desirable specimens exhibit bright hues of blue, green, yellow, orange, or even red. This display occurs due to the interference of light as it hits thin layers within the stone. Labradorite is primarily found in Labrador, Canada, but is also sourced from locations such as Madagascar and Finland.
Value and Rarity: Labradorite is prized for its labradorescence, the brilliant play of color that sets it apart. High-quality Labradorite that displays bright and multiple colors is typically more valuable. Despite its stunning visual effects, Labradorite is fairly abundant and affordable.
Identification: Labradorite is known for its remarkable labradorescence. High-quality samples display bright and multiple colors. The stone’s refractive index and specific gravity can also be measured for more definitive identification.
7. Moonstone
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A gemstone with a storied history, Moonstone belongs to the feldspar group. It exhibits a soft, watery opaqueness and a silvery-white reflection that moves as a line across the surface as light varies, a phenomenon known as adularescence. It often shows areas of blue, pale green, or peach pink, reminiscent of the moon’s glow, hence its name. Major sources of moonstone include India, Sri Lanka, and Myanmar.
Value and Rarity: High-quality Moonstone with a blue sheen is considered more valuable than other varieties. The stone’s overall clarity, size, and the quality of its adularescence significantly contribute to its value. Moonstones from Myanmar are particularly prized for their deep blue sheen.
Identification: High-quality Moonstone exhibits adularescence and a blue sheen. It can be identified by its milky appearance and the floating light effect on its surface. Microscopic examination can reveal the layered structure of the stone.
8. Fluorite
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Known for its wide array of colors and its stunning fluorescence, Fluorite is a versatile mineral. It exhibits color variation based on impurities within the stone and its exposure to radiation. This wide range of colors, combined with its ability to fluoresce brightly under ultraviolet light, makes Fluorite unique. It’s found in various locations worldwide, with notable deposits in China, Mexico, and the USA.
Value and Rarity: Despite its striking range of colors and its ability to fluoresce, Fluorite is fairly common and affordable. However, rare specimens with exceptional color and clarity can command higher prices among collectors.
Identification: Fluorite’s ability to fluoresce under ultraviolet light is a key identification characteristic. It’s also one of the few gemstones that can be four-colored and exhibits perfect cleavage, which can be confirmed under magnification.
9. Tourmaline
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Tourmaline, available in more colors than almost any other gem, has certain varieties displaying pleochroism, which means they show different colors when viewed from different angles. In some cases, one tourmaline crystal can display multiple colors, like the famed “watermelon” tourmaline.
This incredible diversity is due to the complex chemical composition of tourmaline, which allows for various colors and color effects. Major sources include Brazil, Afghanistan, and several African countries.
Value and Rarity: The value of Tourmaline depends on its color, size, and quality. Color-change Tourmaline is quite rare and can be more expensive than other varieties. “Watermelon” Tourmaline, which showcases multiple colors in one crystal, can also be particularly valuable.
Identification: The color-change variety of Tourmaline often switches between green and red. The stone’s dichroic nature can be observed under a dichroscope. It also exhibits strong pleochroism, and its refractive index and specific gravity can be measured for further identification.
10. Ametrine
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A unique variety of quartz, Ametrine, naturally combines the colors of amethyst and citrine. It often presents zones of purple and yellow or orange, giving a striking contrast in the same gemstone. This duality occurs dueto different oxidation states of iron within the crystal, influenced by temperature and radiation exposure during its formation.
Ametrine is quite rare in nature, with the Anahi mine in Bolivia being the major source. Its unique coloration and rarity make it a desirable gem for collectors and jewelry makers alike.
Value and Rarity: Ametrine is prized for its unique combination of amethyst and citrine in a single stone. It’s relatively rare in nature, which adds to its value.
Identification: Ametrine can be identified by its zones of yellow and purple, characteristics of citrine and amethyst respectively. The zoning is usually sharp and can be observed under magnification. Its refractive index and specific gravity can also be measured for more definitive identification.
What Scientific Theories Explain the Color Change in Stones?
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1. Absorption and Transmission of Light
The color of any material is largely determined by how it absorbs, transmits, or reflects light. In the case of certain gemstones, light passing through the crystal structure is selectively absorbed by different elements or compounds within the stone, which can change the color that we perceive.
Alexandrite is an excellent example of this phenomenon. The presence of chromium in Alexandrite causes it to absorb certain wavelengths of light, resulting in a dramatic color change under different lighting conditions.
2. Trace Elements and Impurities
The presence of trace elements or impurities within a stone can significantly influence its color. For instance, the color-change variety of Garnet owes its fascinating color shift to trace elements such as chromium and vanadium. When these elements are present within the crystal lattice of the garnet, they can absorb different wavelengths of light and display different colors under different light sources.
3. Structural Anomalies
The color change in some gemstones is due to structural anomalies within their crystal lattice. For example, in Labradorite, thin layers within the stone refract or bend the light that hits them, producing different colors at different angles. This optical effect is known as labradorescence.
4. Pleochroism
Certain stones, like Tourmaline, exhibit a phenomenon known as pleochroism, where they display different colors when viewed from different angles. This is due to the double refraction of light within the crystal structure of the stone, causing light that enters the stone to split into two rays. Each of these rays interacts with the stone differently, producing different colors depending on the viewing angle.
5. Intervalence Charge Transfer
In certain stones, color change occurs due to a process known as intervalence charge transfer. This is a quantum mechanical process where light is absorbed as electrons jump between different charged ions in the crystal. Diaspore provides a fantastic example of this. The presence of iron ions in Diaspore allows for intervalence charge transfer, leading to a color change under different lighting conditions.
6. Play of Color and Adularescence
Some stones, such as Opal and Moonstone, display color change phenomena due to their unique internal structures. In Opal, this is referred to as a ‘play-of-color,’ caused by diffraction of light passing through tiny silica spheres within the stone. Moonstone displays a similar phenomenon known as adularescence, resulting from light scattering within the stone’s layered structure.
7. Fluorescence and Phosphorescence
Certain stones, like Fluorite, can change color when exposed to ultraviolet light—a phenomenon known as fluorescence. Some stones can even continue to glow after the UV light source is removed due to a process known as phosphorescence.
Conclusion
Stones that change color, with their captivating play of hues, truly showcase the wonders of our natural world. They’re beautiful, rare, and exhibit fascinating scientific phenomena, making them a prized possession for many. The next time you hold a piece of color-changing gemstone jewelry, you’re not just holding a piece of art, but a small piece of nature’s magic.
