Lovely Gemstone Luster - GemSelect Newsletter

Gemstone Luster: Collection of Cabochons

Gemstone luster is perhaps one of the most underrated optical properties when it comes to the appearance of gemstones. It's one of the many terms you'll come across when reading or discussing gems with friends or colleagues. It may not sound so important, but this visible shine (or lack of) can often affect the value of a gemstone just as brilliance and fire can.

Luster is a term that's used to describe how gemstones look or appear, but what exactly is the difference between luster and all the other terms used to describe the appearance of gemstones? Luster refers to the way light reflects from the surface of a gemstone. It's essentially the opposite of brilliance, which is the way light reflects from the interior of a stone.

Pearls, cabochons, and opaque gemstones are usually graded by luster, whereas faceted gems are typically graded by their brilliance. However, even faceted stones can lack the shiny luster and appearance without a good polishing. This is why it's important that every gemstone is given an excellent polish in order to get the most value out of them. A poorly polished gem will simply lack the lustrous look as one that has been given an expert polishing.

Pyrite With Metallic Luster

When it comes to minerals, there are only two main types of luster: metallic and non-metallic. Unfortunately, when it comes to gemstones, it's not that simple. From bright to dull, gemstone luster terms include: metallic (pyrite and hematite), submetallic (sphene and melanite), adamantine, subadamantine, vitreous, changeable, pearly, silky, resinous, greasy, waxy, and dull.

Aquamarine With Vitreous Luster

Adamantine luster is typically the most prized luster since it's associated with the high luster of diamond. There are only a handful of gemstones known to exhibit such a high level of luster; examples include zircon, demantoid garnet, and sphene.

Indeed, these gemstones do exhibit an incredible and attractive shine, but there are many gemstones with non-adamantine luster that are just as stunning and often more valuable. For example, the luxurious luster of pearls is beyond compare, as is the greasy luster seen in many varieties of jade.

Blue Zircon with Adamantine Luster

Despite the negative connotations with glass, when it comes to luster, glass is more than acceptable. Vitreous luster is described as being glassy or glass-like. Many of the world's most highly-valued gemstones exhibit a vitreous luster, including ruby, sapphire, and emerald. Other gems with vitreous luster happen to be some of the most popular gemstones, such as topaz, beryl, and spinel.

Ruby With Glass-Like Vitreous Luster

One of the most intriguing forms of luster is a changeable luster. Changeable luster is an altering luster that can be seen in many different types of phenomenal gemstones, including moonstone, cat's eye, ammolite, labradorite, and spectrolite. These phenomenal gems exhibit a different 'changeable' luster depending on how or where they're viewed.

For example, ammolite and labradorite alter luster as they are rotated and tilted back and forth or side to side. Under focused light, cat's eyes and star gemstones display asterisms that appear to glide across the stone as they're turned and tilted, similar to the way light reflects off a string of gleaming silk.

Labradorite with Changeable Luster

Pearly and silky gemstone luster are quite attractive, perhaps even more so that many vitreous or adamantine gemstones. Gemstones which fall under these luster grades are usually cabochons, although fine materials are sometimes faceted.

Gemstones with pearly luster include those which exhibit iridescence. Some examples include the shimmer seen in fine charoite or rough moonstone, as well as mother of pearl and abalone. Silky luster is often confused with pearly luster, but gems with a silky luster display various forms of simple chatoyancy rather than iridescence. Silky gemstones include tiger's eye and other types of fibrous gems, such as hawks eye, pietersite, malachite, and ulexite.

Silky and Chatoyant Charoite

Gems with waxy luster have a dull shine that appears to be the result of a waxy coating. These include many types of opal and turquoise, as well as flint. Chrysoprase and coral also have a waxy luster, although coral's luster can range from dull to vitreous. Gems with resinous luster appear slightly less glossy and a bit more sticky than those with waxy luster. The best example of a gemstone with a resinous luster would be amber, especially since amber actually is a form of preserved prehistoric resin.

Greasy gemstone luster is just as it sounds; a luster that appears to have an oily or fatty coating. Gemstones with a greasy luster includes nephrite (Hetian seed-jade), jadeite, and peridot. When it comes to dull gemstone luster, there are actually very few materials which exhibit a dull luster; these would include rhodonite or rough turquoise.

Seraphinite Can Have Pearly, Vitreous, or Greasy Luster

Luster can sometimes be used to help to identify gemstone types. To properly inspect the luster of a gemstone, ensure that it’s clean and free from any coating or tarnish. It is best to observe the gem under good lighting at angles which allows light to reflect to and away from the eye.

Since gemstone luster lacks a definite measurement, it is not the most reliable method for identification. However, it can still be helpful if trying to distinguish gems with an adamantine or vitreous luster from those with a greasy or resinous luster.

Ruby is July's official birthstone and it's one of the most treasured and valuable gemstones in the world. It's rare to find fine quality Burmese ruby in any shape or size, but round rubies are especially hard to source. We were very fortunate to source many beautiful round-shaped rubies from Burma this month, including large singles, matching pairs, and matching lots.

Red Ruby from Burma

Clinohumite is not a gemstone that many peope have even heard of, but for those who have, they know how rare and unusual this fantastic collector's gem truly is. Since there are only three known sources for gem-quality clinohumite (Tajikistan, the Taymyr region in Siberia, and Tanzania) we consider ourselves very lucky to have found such a wonderful rarity.

Rare Clinohumite Gemstone

Hessonite garnet is one of the many awesome gemstone varieties of garnet. More specifically, hessonite belongs to the grossularite family. Other types of grossularite include rare Tsavorite and exotic Mali garnet. In the world of Jyotish or Vedic astrology, hessonite garnet is known as 'Gomed', one of the nine planetary gemstones of Navaratna.

Hessonite Garnet

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