The corundum mineral family stands as a titan in the world of gemstones, celebrated for its exceptional hardness and vibrant colours. This remarkable mineral family encompasses a range of prized gems, most notably the fiery ruby and the enchanting sapphire, each possessing unique characteristics that have fascinated civilisations for millennia.
Among the most coveted varieties are the mesmerising blue sapphires (neelam) and yellow sapphires (pukhraj), the radiant star sapphires with their captivating asterism, and the fiery red rubies, each a testament to the captivating beauty and enduring appeal of the corundum family.
In this blog, we will explore the captivating world of corundum, delving into its chemical composition, physical properties, geological origins, and the intricate factors that contribute to the breathtaking beauty of this extraordinary mineral family.
1. Formation & Occurrence
Corundum, the crystalline form of Aluminum Oxide (Al2O3), emerges from the depths of the earth through intricate geological processes. This remarkable mineral typically forms under intense heat and pressure, often within metamorphic rocks such as gneiss and schist or in igneous rocks like syenite and pegmatite. The very foundation of corundum lies in its chemical composition, with aluminum oxide serving as its primary building block. This unique arrangement of aluminum and oxygen atoms contributes to corundum's exceptional hardness, ranking it 9 on the Mohs scale, second only to diamond.
The presence of trace elements like chromium, iron, and titanium during the corundum's formation introduces a kaleidoscope of colours, which is the primary component of its classification into different varieties of gemstones. For example, the blue color of blue sapphires is often attributed to the presence of titanium and iron, while the fiery red of rubies arises from chromium.
2. Global Deposits of Corundum
Corundum is scattered across the globe, with each location contributing unique characteristics to the gemstones it yields. Sri Lanka, renowned for its "Ceylon Sapphires," boasts a rich history of producing exquisite blue and yellow sapphires. Myanmar, formerly Burma, is legendary for its Pigeon's Blood rubies, celebrated for their exceptional colour and clarity. Thailand, particularly the Chanthaburi and Trat areas, is recognised for its significant sapphire production, often yielding gems in a range of blue and yellow hues.
Madagascar has emerged as a major player in the corundum market, offering a diverse array of sapphires, including blues, pinks, yellows, and colour-change varieties. Other notable sources of corundum include Kashmir, known for its velvety blue sapphires, and Tanzania, which produces an array of sapphires and rubies. Australia, Vietnam, and the United States also contribute to the global corundum supply, adding to the diverse tapestry of these captivating gemstones.
3. The Colour Spectrum of Corundum
Corundum's captivating beauty stems from its remarkable spectrum of colours, this diverse palette arises from the presence of trace elements, or impurities, nestled within the corundum crystal lattice. For example, chromium, the trace element behind rubies, imbues them with their signature red hue. The intensity of the red deepens with the concentration of chromium, culminating in the coveted "Pigeon's Blood" red. Iron and titanium, on the other hand, orchestrate the symphony of blues and yellows in sapphires. Their intricate interplay within the crystal structure determines the specific shade, ranging from delicate sky blues to deep, velvety indigos.
Corundum occurs in almost every shade of the rainbow
4. Varieties of Corundum
The corundum family boasts two reigning monarchs in the gem world: the ruby and the sapphire. Each possesses unique characteristics and a rich history that has captivated civilisations for centuries.
Ruby
Defined as red corundum, the ruby is a gemstone of passion, power, and prestige. Its colour, ranging from deep crimson to vibrant cherry red, is attributed to the presence of chromium within the crystal lattice. Myanmar, formerly Burma, is renowned for its "Pigeon's Blood" rubies, considered the epitome of ruby perfection due to their exceptional colour and clarity. Other significant ruby sources include Mozambique, Madagascar, and Vietnam. Rubies have a long and illustrious history, adorning the crowns of royalty and the regalia of empires. In addition to their cultural and historical significance, rubies are also valued for their durability, ranking just below diamonds on the Mohs scale of hardness. This durability, coupled with their vibrant color and rarity, makes rubies highly sought after in the world of fine jewelry.
Rubies can occur in a colour span from light pink to a deep & vivid red
Sapphire
While sapphires are most commonly associated with the color blue, they occur in almost every shade of the rainbow, each with its unique charm and beauty. Some of the most important types of sapphires, classified according to their colors, are:
- Yellow Sapphire (Pukhraj): Ranging from pale lemon to rich golden, yellow sapphires are believed to attract wealth, prosperity, and abundance.
- Blue Sapphire (Neelam): The classic blue sapphire, ranging from delicate sky blue to deep indigo, is revered for its wisdom, loyalty, and spiritual connection.
- Pink Sapphire: With hues ranging from soft blush to vibrant fuchsia, pink sapphires embody love, compassion, and emotional healing.
- Green Sapphire: Evoking the lushness of nature, green sapphires symbolise growth, renewal, and prosperity.
- Bi-Color Sapphire (Parti Sapphire): These unique sapphires showcase a mesmerising blend of two or more colors, often blue and yellow or blue and green.
- White Sapphire: Colorless and transparent, white sapphires are known for their purity and clarity and are often used as diamond alternatives.
- Other Sapphires: Sapphires can also occur in a range of rainbow hues, including purple, orange, brown, and grey.
Color spectrum of sapphires
5. Common Inclusions in Corundum
Corundum gemstones, such as rubies and sapphires, often contain various inclusions that contribute to their unique character and beauty. Here are some of the most common inclusions found in corundum:
- Rutile Needles: Delicate, hair-like inclusions that can create a silky sheen. When densely packed and properly oriented, they produce a shimmering asterism effect, as seen in star sapphires.
- Fingerprints: Named for their resemblance to human fingerprints, these intricate patterns are often formed by healed fractures within the crystal, adding a unique texture to the gem.
- Mineral Crystals: Inclusions of other minerals such as spinel, garnet, or zircon, these can sometimes be visible to the naked eye and may add a subtle sparkle or color variation to the gem.
- Feathers: Fracture patterns that resemble feathers, often white or transparent. These inclusions can impact the gem's clarity and are usually visible under magnification.
- Needles: Thin, elongated inclusions that can be made of various minerals, Depending on their orientation and density, needles can either enhance or detract from the gemstone's appearance.
- Crystal Clusters: Groups of tiny crystals trapped within the corundum during its formation. These clusters can create interesting visual effects and may affect the stone's transparency.
Common inclusions in Corundum (Source: GIA)
Understanding these inclusions helps gemologists and enthusiasts appreciate corundum gems' origin, formation history, and unique characteristics.
6. Treatments & Enhancements of Corundum
Corundum gemstones, while naturally beautiful, often undergo various treatments and enhancements to elevate their colour, clarity, and overall appearance.
- Heat Treatment: Heat treatment is the most common and widely accepted practice. It involves exposing corundum to high temperatures, which can intensify colour, improve clarity by dissolving inclusions, and remove undesirable colour zoning.
- Diffusion Treatment: Another common enhancement is diffusion treatment, where trace elements like titanium or beryllium are introduced to the gemstone's surface during heating. This treatment can create or intensify colours, particularly in sapphires, by diffusing these elements into the gem's outer layers. While diffusion treatment can produce striking results, it is often less valued than natural or heat-treated stones due to its surface-limited nature.
- Fracture Filling: Fracture filling is a technique used to enhance clarity by filling surface-reaching fractures with substances like glass or resin. This treatment can significantly improve the appearance of heavily included or fractured stones, making them more visually appealing. Fracture-filled stones are generally less valuable than their untreated or heat-treated counterparts due to the impermanence of the enhancement.
7. Evaluating the Quality of a Corundum Mineral
Identifying and grading corundum involves a meticulous evaluation based on the four key factors known as the 4Cs:
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Color: The most crucial factor in grading corundum is undoubtedly color. It is primarily based on optics and color that the different corundum gems are classified. If a corundum is red, it is classified as a ruby, while a blue corundum is known as a Neelam. Other hues like yellow, pink, and green are referred to as "yellow sapphire," "pink sapphire," and so on.
For rubies, the intensity and purity of the red hue, along with any secondary colors, determine their value. The most coveted color is a deep, vibrant red with a hint of blue, often referred to as "Pigeon's Blood." Blue sapphires, on the other hand, are graded based on their hue, tone, and saturation. The most prized blue sapphires exhibit a "Royal Blue" or a "Cornflower Blue" color. The evenness of color distribution and the absence of undesirable color zoning also play a significant role in determining a corundum gem's value.
- Clarity: Clarity refers to the presence or absence of inclusions within a gemstone. High-clarity corundum gems, free from eye-visible inclusions, are more valuable than heavily included stones.
- Cut: The cut of the gemstone plays a significant role in its overall appearance and value. Corundum gems are typically cut into various shapes, including oval, round, cushion, and emerald cuts, to enhance their natural beauty.
- Carat Weight: Carat weight, while not as critical as colour and clarity, influences the gem's value, with larger stones commanding higher prices per carat.
The interplay of colour, clarity, cut, and carat weight, along with its characteristic luster and specific gravity, determines a corundum gem's worth
8. Corundum Gems in Astrology
In astrology, corundum gems hold significant meaning and are believed to influence various aspects of life based on their unique properties. Different varieties, such as rubies, blue and yellow sapphires, are associated with distinct celestial bodies and astrological benefits, each offering unique energies and attributes to their wearers.
Rubies, for example, are linked with the Sun and considered auspicious for Leos in Vedic astrology. They are believed to enhance vitality, courage, and leadership qualities, empowering the wearer with confidence and determination. Blue sapphires (neelam stone), on the other hand, are associated with Saturn and are beneficial for Capricorns and Aquarians. These gems promote mental clarity, discipline, and spiritual growth while protecting from negative energies. Further, yellow sapphires (pukhraj), connected with Jupiter, symbolise wisdom, prosperity, and spiritual growth. They are thought to bring abundance and good fortune to Sagittarius and Pisces, enhancing optimism and intuition for success and personal fulfilment.
Beyond these well-known varieties, other types of corundum such as green sapphires, parti-sapphires, and pitambari sapphires also carry unique astrological properties. These gemstones are often used in astrological remedies and talismans to harness their purported metaphysical properties, balancing astrological energies and enhancing the wearer's life in specific ways.
In conclusion, the corundum family stands as a testament to nature's enduring beauty and the marvels of geological processes. As we delve deeper into the intricate beauty and rich history of the corundum family, we gain a deeper appreciation for these timeless treasures, which have stood the test of time and continue to shine brightly in the realms of art, science, and spirituality.
