The sparkle is produced by the interaction of light and the diamond’s surface, and is what gives the diamond its signature shine. Scintillation refers to the sparkle that is created when light is reflected off of the facets of a diamond. A diamond with good fire will have a vibrant and colorful display of light. Fire is what makes a diamond appear sparkling and is often used to describe the diamond’s brilliance. This light is a result of the diamond’s ability to bend and reflect light, creating a rainbow of colors. A key aspect of a diamond's beauty is its fire and scintillation, two features that contribute to the unique sparkle of the stone.įire refers to the colorful light that is dispersed from a diamond when it is exposed to light. Since judgment of beauty is by definition subjective, quality of cutting is also a matter of opinion.Diamonds are one of the most sought-after gemstones in the world, prized for their beauty and brilliance. What works best is simply what works best-that which brings out the greatest beauty in the gem. It is important to note that gem cutting is an art form rather than a formula. Overly-deep stones have the double disadvantage of being more difficult to set in jewelry. The main thing to look for stones that are of good proportions-not too shallow, nor too deep. Thus, one should not worry too much about RI. But as we learned with luster, a high RI can actually hurt the display of color. Again, brilliance suffers (and there's nothing worse than suffering brilliance).Ī gem's potential brilliance is mainly a function of refractive index (RI), with higher RI gems having more potential brilliance.

This creates areas of darkness, known as extinction. Similarly, if the gem is cut too deep, light from above passes out the side. This created a window where one can see through the gem. If the gem is cut too shallow, light from above and below passes straight through. Faceted gems are designed to catch all possible light and throw it back to the eye. This is why the colors of high refractive index (RI) gems, such as diamonds, are often somewhat 'steely' while the colors of lower RI gems, such as emerald, can be so beautiful.īrilliance refers to the amount of light returned to the eye from the interior of a gem and is mainly a function of refractive index, proportions and transparency. Certainly for colorless gems such a diamond, this is the case, but for gems that depend on their color for beauty, a high luster is actually an impediment since it prevents light from entering the gem. Examples include muscovite, talc and the shell of various mollusks.Ī common misconception is that high luster is better. Pearly: As this adjective implies, it is descriptive of the luster seen in pearls and is used to describe any mineral or gem that has a similar appearance. Examples include ulexite, gypsum and malachite. Silky: This type of luster is characteristic of certain gems that have an extremely-fine fibrous structure. It has the appearance of polished plastic. Resinous: This luster is characteristic of certain gems with low-to-moderate refractive indices. Vitreous: This luster is seen in polished glass and in most transparent gemstones whose refractive indices fall within the middle range of values (e.g., emerald and tourmaline). Subadamantine: This term is used to describe gems that have a bright luster approaching that of diamond (e.g., certain varieties of zircon and garnet). It is characteristic of gems with higher refractive indices (e.g., diamond and demantoid garnet). Īdamantine: This is the brightest, most reflective non-metallic luster. Sphalerite and cuprite often exhibit this type of luster. Nearly-opaque gems that reflect well fall into this category. Submetallic: This is used to describe minerals having the look of polished metal dulled by weathering or wear. Hematite, pyrite and cuprite are examples of minerals that may exhibit this degree of luster. Metallic: This is a very high luster that has the appearance of polished metal. Luster is generally divided into two major categories: metallic and non-metallic.Īdjectives commonly used to describe luster include: If much of the light is absorbed b the gem, resulting in a dull reflection, it is said to have low luster. If nearly all the light falling upon a gem's surface is reflected, resulting in a very bright appearance, it is said to have high luster. Luster is the quality and quantity of light reflected from a gem's surface and is a function of refractive index and surface perfection (degree of polish). The following clears up the confusion, allowing you to understand exactly what you are seeing when you gaze upon your gemstone jewelry. These frequently used terms describe the visual appearance of the interaction between light and a gem are often confused and misused, sometimes even by experienced industry professionals.

Fire and brilliance gemstone