Sapphires are among the most prized and cherished gemstones in the world. Known for their striking beauty and significant hardness, they are used in a variety of jewelry pieces. However, there is a special subset of sapphires known as star sapphires that are distinguished by their unique optical phenomenon known as asterism. This article will explore the differences between regular sapphires and star sapphires in detail.
Definition
Sapphire:
A sapphire is a gemstone variety of the mineral corundum, an aluminum oxide (Al₂O₃). It is most commonly recognized for its vibrant blue color, although it can occur in a variety of colors except for red, which is classified as ruby. Sapphires are highly valued for their exceptional hardness (second only to diamonds), durability, and brilliance, making them ideal for all types of jewelry.
Star Sapphire:
A star sapphire is a unique variety of sapphire that exhibits a star-like pattern on its surface, known as asterism. This phenomenon occurs due to the presence of needle-like inclusions of the mineral rutile. When cut as a cabochon, these inclusions reflect light in a star pattern, typically with six rays, although star sapphires with four, twelve, or even twenty-four rays can occur. The star moves across the stone as it is tilted, adding an intriguing dynamic quality to the gemstone.
Appearance
Sapphire:
Regular sapphires are typically faceted to enhance their brilliance and maximize light reflection. The classic cut styles for sapphires include oval, round, cushion, and emerald cuts. Their appearance can vary widely depending on the quality of the stone, with the finest sapphires exhibiting a deep, vivid blue hue, often described as “cornflower blue.” Other color variations include pink, yellow, green, white, and purple, referred to as “fancy sapphires.”
Star Sapphire:
Star sapphires, on the other hand, are primarily cut into cabochons to best display the asterism. A cabochon cut means the stone is shaped and polished into a smooth, rounded dome rather than faceted. The quality of a star sapphire is judged based on the sharpness, symmetry, and visibility of the star, as well as the overall color of the stone. The background color of star sapphires can also vary widely, but blue and black are the most common.
Asterism
Sapphire:
Regular sapphires do not exhibit asterism. Their beauty lies in their color, clarity, and sparkle, which is enhanced through faceting.
Star Sapphire:
The defining feature of star sapphires is their asterism. This star-like effect is created by the reflection of light off the rutile needle inclusions within the stone. The inclusions must be oriented in such a way that they reflect light in a star pattern, which is why the cabochon cut is used. The star effect is most visible under direct light, where it appears to glide across the surface of the stone as it is moved. The best star sapphires have a sharp, well-defined star with straight, evenly spaced rays that extend from the center of the stone to the edges.
See Also: What Should Not Be Worn with Sapphire?
Color and Qualification
Sapphire:
The color of a sapphire is one of the most important factors in determining its value. The most prized color is a deep, vivid blue, often referred to as “royal blue” or “cornflower blue.” The color should be evenly distributed throughout the stone without zoning. Other colors, or “fancy sapphires,” are also valued, though typically not as highly as blue sapphires. These include pink, yellow, green, purple, and even colorless varieties. The presence of trace elements like iron, titanium, chromium, copper, or magnesium gives sapphires their range of colors.
Star Sapphire:
Star sapphires also come in a variety of colors, with blue and black being the most common. The quality of a star sapphire is judged not only by its color but also by the clarity and visibility of the star. The most valuable star sapphires have a strong, sharply defined star that contrasts well against the background color of the stone. While blue star sapphires are highly prized, star sapphires in other colors, such as pink, purple, and even white, are also sought after by collectors and gem enthusiasts.
Clarity
Sapphire:
Clarity refers to the presence of inclusions or blemishes within the gemstone. For regular sapphires, higher clarity generally increases the value, as inclusions can detract from the stone’s overall appearance and brilliance. The most valuable sapphires are those that are eye-clean, meaning they have no inclusions visible to the naked eye. Common inclusions in sapphires include needle-like rutile inclusions, often referred to as “silk,” which can sometimes enhance the stone’s overall appearance by giving it a velvety texture.
Star Sapphire:
In star sapphires, inclusions play a crucial role in the formation of the star effect. The rutile needles that cause asterism are necessary for creating the star pattern. Therefore, the presence of these inclusions is not only acceptable but essential. However, the overall clarity still matters; the stone should be free from other types of inclusions that might cloud the stone or interfere with the visibility of the star. A high-quality star sapphire will have well-oriented rutile inclusions that create a sharp, distinct star, with minimal other inclusions to ensure the background color remains as vibrant and clear as possible.
Origin
Sapphire:
Sapphires are found in several locations around the world, each producing stones with unique characteristics. Historically, Kashmir sapphires are considered some of the finest due to their exceptional color and clarity, often exhibiting a velvety blue hue. Burmese (Myanmar) sapphires are also highly prized for their rich blue color. Other notable sources include Sri Lanka (Ceylon), known for a variety of colors including the famous cornflower blue, Madagascar, Thailand, Australia, and the United States (Montana).
Star Sapphire:
Star sapphires are also mined in various locations around the world. Sri Lanka is a major source, producing star sapphires in a range of colors, particularly blue and black. Myanmar is known for high-quality blue star sapphires. Thailand and Australia are also significant sources, with Australia producing a considerable amount of black star sapphires. Madagascar has emerged as an important source for both regular and star sapphires in recent years. The geographic origin can influence the color, quality, and overall value of the star sapphire, much like regular sapphires.
Conclusion
In summary, while both regular sapphires and star sapphires share a common mineral composition, they differ significantly in appearance, value determinants, and physical properties. Regular sapphires are prized for their color, clarity, and brilliance, typically enhanced through faceting. Star sapphires, distinguished by their unique asterism, are most valued for the sharpness and visibility of their star pattern, best showcased through a cabochon cut. The inclusions that would typically decrease the value of a regular sapphire are crucial for the beauty and uniqueness of a star sapphire. Understanding these differences can help gemstone enthusiasts and buyers make informed decisions when selecting these captivating gemstones.
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