Why the Confusion Between Ruby and Garnet?
Rubies and garnets are popular red gemstones, often presenting a challenge for individuals attempting to distinguish between them. Both gems exhibit beautiful red hues, leading to frequent misidentification. This article aims to clarify the differences, providing guidance for identification.
Both gemstones occur in various shades of red, ranging from deep, rich crimson to lighter, more purplish or orangish-red tones. Historically, before the advent of modern gemology, many red gemstones were simply referred to as “carbuncles” or “rubies,” leading to garnets often being mistaken for or even sold as rubies. While they may appear alike to the casual observer, rubies and garnets are distinct mineral species with differing chemical compositions and crystalline structures.
Key Scientific Distinctions
A fundamental difference between these two red gemstones lies in their hardness, measured on the Mohs scale. Ruby, a variety of the mineral corundum, has a Mohs hardness of 9.0, making it exceptionally durable. Garnets, a group of silicate minerals, typically range from 6.5 to 7.5 on the Mohs scale, making them generally softer than rubies and less resistant to scratching.
Another distinguishing property is refractive index (RI), which describes how light bends as it passes through a gemstone. Ruby typically has a refractive index range between 1.762 and 1.770, often exhibiting a bright, adamantine (diamond-like) luster. Garnets, depending on their specific variety, show a wider RI range, generally from 1.714 to 1.889, and often display a vitreous (glassy) luster. This difference affects how light interacts with the stone, influencing its overall appearance.
Fluorescence, the emission of light by a substance when exposed to ultraviolet (UV) radiation, is a key differentiator. Many rubies, especially those from certain origins, exhibit a strong red to orangish-red fluorescence under long-wave UV light due to the presence of chromium. In contrast, most common garnet varieties do not fluoresce under UV light.
Internal characteristics, known as inclusions, differ between the two gemstones. Rubies often contain fine, needle-like rutile inclusions, sometimes referred to as “silk,” which can create a soft, hazy appearance or a star effect. Garnets frequently display different types of inclusions, such as internal fractures, small crystals, or “horsetail” inclusions in some demantoid garnets. Specific gravity, or density, also differs; rubies are generally denser than garnets, with a specific gravity of around 3.97-4.05 compared to garnet’s 3.4-4.3.
Practical Home Identification Methods
Observing the gemstone’s color and luster can provide initial clues. Rubies often possess a purer, more vibrant red color, sometimes described as “pigeon’s blood red,” and typically display a brighter, more fiery sparkle. Garnets, while also red, might lean towards brownish, orangish, or purplish undertones and generally exhibit a more subdued, glassy sheen. Using a jeweler’s loupe (10x magnification) can help in discerning these subtle visual differences and examining the stone’s surface.
A cautious “scratch test” can indicate hardness, but it should be performed with extreme care on an inconspicuous area of the stone to avoid damage. While both ruby and garnet can scratch glass (Mohs 5.5), a ruby (Mohs 9) will scratch a topaz (Mohs 8), whereas a garnet (Mohs 6.5-7.5) will not. This method carries a significant risk of damaging the gemstone, and it is generally not recommended for valuable pieces.
Using a long-wave UV flashlight can help assess a gemstone’s fluorescence. Place the stone under the UV light in a darkened room and observe if it glows. If the gemstone is a ruby, it may emit a distinct red or orange glow. Most garnets, however, will show no reaction or a very weak one under UV light.
Examining inclusions under magnification, such as with a jeweler’s loupe, can reveal characteristic patterns. Look for fine, silky rutile needles within the stone, which are common in rubies. Garnets might show different types of internal features, such as small, rounded crystals or fractures. Holding the stone and assessing its perceived weight can offer a slight indication; a ruby of the same size might feel marginally heavier than a garnet.
When Professional Assessment is Necessary
While home identification methods can provide strong indicators, they are not definitive. For accurate and conclusive identification, especially for valuable or heirloom pieces, consulting a certified gemologist is necessary. Gemologists utilize specialized laboratory equipment, such as refractometers, spectroscopes, and high-powered microscopes, to precisely measure optical properties and analyze internal structures. These professional assessments ensure accurate identification and can provide detailed reports, invaluable for insurance or when considering buying or selling a gemstone.