In addition to color and luster, luster is an optical property that can make gems beautiful.

This characteristic is often described as giving certain gems a "mysterious" appearance.

In the ancient world, a kind of lustrous gemstone belonged to the gods and was thought to confer magical powers.

Luster-caused by the light reflection of the internal inclusions of the gem-appears in many forms in the gem world, each with a different gemological name.

For example, iridescence is the form of luster that makes moonstone and labradorite so attractive to our eyes.

Two unusual and interesting forms of gloss are starlight and halo.

Gemstones that show starlight and luminous light contain inclusions that reflect light in a specific way.

The arrangement of these inclusions will determine whether the gemstone shows starlight or starlight.

If we look at gems and see stars, this form of luster is called starlight.

This word comes from the ancient Greek word aster, which means "star".

The gems that show starlight are highly sought after by collectors.

The type of gem, the clarity of the stars, and the number of star points—4, 6, or 12—are factors that affect their value.

In order to highlight the stars and show their best results, the cutter will shape the gems into cabochons.

Sapphire and ruby, diopside, garnet and rose quartz can show starlight.

When there is an asterisk, the naming of gems uses "star" as a prefix, followed by the name of the gem, for example, star-shaped sapphire or star-shaped ruby.

Starlight occurs when light is reflected by the inclusion of fine crystals or fibers oriented at a specific angle.

In star sapphire, fine needles of hematite or rutile intersect at an angle of 60 degrees.

In starlight diopside, the fibers intersect at an angle of 73 degrees.

As the direction of the gem changes, the light will move on the surface. In turn, the intensity and brightness of the star will also change.

Halo refers to the luster produced by light reflected by parallel channels, crystals, or fibers contained in a gem.

The word chatoyancy comes from the French term oeil de chat, which means "cat's eye".

The shiny gem shows a bright band of reflected light on its surface.

Just as the cat’s eye seen at night shows a line that changes with its movement, when the gem moves under the light source, the ring on the luminous gem also changes its position.

In order to highlight the cat's eye effect, the cutter will use a cabochon cut.

Many gems can show opals, including tiger's eye-a member of the quartz gem family-chrysotile, emerald and tourmaline.

The naming method of Chatoyant gems is to use the gem name first, and then use the term "cat's eye" as a suffix, such as tourmaline cat's eye or golden emerald cat's eye.

Luster is an important optical property that contributes to the beauty, value and attractiveness of many gems.

Starlight and Luminous are the two forms of luster that make the gem world so exciting and alluring.

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Susan Hartwig FGAA combines her love of writing with her passion for gems and jewelry through her gemology blog ellysiagems.com. For more information on gemology courses and gems, please visit: gem.org.au