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Gemstone Luster

When it comes to describing a gemstone’s appearance, luster refers to how a gem’s surface looks when it reflects light.

By Christopher Clark, GG, FGA, ASG, Gemologist & Co-Editor of The Sisk Gemology Reference | JTV
Published: 04/01/2020
Modified: 07/01/2021
gemstone-luster
Gemstone Luster
Table of Contents
  • What is Luster?
  • Types of High Luster
  • Types of Low Luster

What is Luster?

When it comes to describing a gemstone’s appearance, luster refers to how a gem’s surface looks when it reflects light. Gems and minerals exhibit a wide range of lusters, from the reflective metallic luster of polished silver to the entirely non-reflective earthy luster of clay.
Some minerals can exhibit a wide range of lusters, such as malachite. When crystalline, malachite can have a bright adamantine or moderate vitreous luster. When fibrous it can give a silky appearance and massive varieties are usually dull or earthy regarding luster.

 

All About Luster & Gemstones (source: Gemstones.com YouTube)

What gemstone luster is the most common?

The most common luster amongst gemstones is a vitreous luster. This is the luster of most glass and is an easy reference point for determining whether a gem or mineral has a higher or lower luster than vitreous as glass.

Why is luster important?

Luster can be a handy observational property to identify because gemstones with a high luster typically have high refractive indices, and polished gems with lower lusters usually, but not always, have lower refractive indices.

Did you know…? Glittering refers to the luster of the gold, or the quality of the light that is reflected from its surface. Raw gold out of the ground typically has a dull luster that barely reflects at all, compared to its bright metallic luster when polished.

Types of High Luster

The following qualities of luster are typically considered to be higher or brighter in reflective quality than glass:

two metallic squared gold pyrite
Metallic

A highly reflective, often mirrorlike luster

Example Shown: Pyrite

round oval cut gray hematite
Sub-Metallic

Not quite as reflective as metallic

Example Shown: Gray Hematite

round brilliant cut white diamond
Adamantine

A bright, hard reflective brilliance

Example Shown: Diamond

oval cut blue sapphire
Sub-adamantine/Bright vitreous

Brighter than glass, but not quite adamantine

Example Shown: Blue Sapphire

brilliant cut rhodolite garnet
Vitreous

The most common luster among gemstones and the luster of most glass (additives in manmade glass can cause a higher or lower luster)

Example Shown: Rhodolite Garnet

Types of Low Luster

The following qualities of luster are typically considered to be lower or of a less reflective quality than glass:

white pearl earrings set in rose gold
Pearly

Similar to mother of pearl, though iridescence may not be present
Example shown: Shell Pearl Earrings

 

round shaped tiger's eye beads necklace
Silky

A shiny, fibrous quality
Example shown: Tiger’s Eye Beads

orange uncut amber specimen with bug inside
Resinous

A resinous or plastic appearance
Example shown: Amber

oval cut blue turquoise
Waxy

Somewhat dull, but still has a slight reflective quality
Example shown: Turquoise

oval shaped brown opal
Greasy

A greasy luster; appears grease or oil coated
Example shown: Brown Opal

unpolished and uncut blue turquoise specimen
Dull

Reflect very little or not at all
Example shown: Unpolished Turquoise Specimen

multi-colored polymer clay beads
Earthy

Even less reflective than dull, but with a coarser appearance, like soil
Example shown: Polymer Clay Beads

More Gemstone Articles

Gemstone Dispersion

Dispersion is the display of color in a gemstone and may be classified as not observable, moderate, strong or very strong.

Gemstone Dispersion

Optical Properties

Learn the optical properties of gemstones including play of color, star and cat's eye.

Optical Properties

Gemstone Transparency

Determining whether your gemstone is transparent, translucent or opaque will help you catalogue your gemstones.

Gemstone Transparency

Evaluating Gemstone Color

Gemstone colors can be amazing, yet most people are unable to explain why we see these rich, vibrant hues.

Evaluating Gemstone Color
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