search
  • Sign In
    Sign Up
  • English speaking customer support only

    1-800-464-1640

  • Change Language
  • USD
By Gavin Clarke Reviewed By Andreas Zabczyk Oct 22, 2008 Updated Jan 24, 2019

Seeing Gemstone Stars

Gemstones that display the star effect, known as asterism, have been valued by connoisseurs for centuries. The best-known examples are star sapphire and star ruby. Asterism may also be found occasionally in a number of other gems, including moonstone, quartz, spinel, citrine, diopside, emerald, garnet, chrysoberyl and sunstone.

Natural Star Gemstones
Natural Star Gemstones

First-time buyers of these star gems sometimes have unrealistic expectations about how sharp and clear the star should appear. Many people have seen synthetic star gemstones with very sharp stars that display perfectly under any kind of light. But this is not the standard by which natural star gems should be judged. To fully appreciate the marvel of a natural star gemstone, it is worth understanding how stars form in natural gems, and how best to observe the asterism.

The essential element in producing a star gemstone is the mineral rutile. If inclusions of rutile are densely packed, and aligned in the correct way, then they will reflect light in a multi-rayed pattern, forming a star. The gem must be cut as a cabochon in order to display a star, and it must have the right proportions; neither too flat on the top nor too heavy on the bottom.

Star gemstones tend to be opaque or translucent rather than transparent, due to the rutile inclusions. This often affects the color of the gem. In fact, there is a trade-off between the distinctness of the star and the saturation of the body color. More rutile means a more distinct star, but a somewhat muddier color. Since color is also very important in these star gems, cutters try to strike a balance between the star and the body color when selecting their material.

Star Moonstone
Star Diopside
Star Sunstone
Star Sapphire
Star Moonstone Star Diopside Star Sunstone Star Sapphire

Most natural star gems display a star only in sunlight or in strong indoor light. Even very good quality stars show poorly in diffused light. A focused light displays the star best, and all photos you see of these stones will be taken under such lighting. Gem dealers use a penlight to evaluate star gems. The trick is to hold the light about 15 cm (6 inches) above the stone. Move the light back and forth to see how the star moves across the surface of the stone. The star should be sharp and clear, and the rays should be straight and evenly spread. The star should be centered at the top of the dome, and it should extend across the entire stone. It should travel easily across the surface of the cabochon as you move the light back and forth.

Some natural star sapphires are enhanced by a process that diffuses rutile into the gem to improve the star. The treatment is permanent and produces good results. Most star rubies are not diffusion-treated to improve the star, but some are fracture-filled.

STAY IN TOUCH
*You're signing up to receive GemSelect promotional email.
Partners and Trust Payment options

Switch to Mobile Version

Privacy Notice © 2005-2023 GemSelect.com all rights reserved.

Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.

646

More Shapes
Popular Gemstones
  • Sapphire
  • Emerald
  • Ruby
  • Aquamarine
  • Zircon
  • Opal
  • Topaz
  • Tourmaline
  • Garnet
  • Amethyst
  • Citrine
  • Tanzanite
All Gemstones (146)
A B C D E F G H I J K L M N O P Q R S T V Z
  • Actinolite Cat's Eye
  • Agate
  • Agate Geode
  • Almandine Garnet
  • Amazonite
  • Amethyst
  • Amethyst Geode Slice
  • Ametrine
  • Ammolite
  • Andalusite
  • Andesine Labradorite
  • Apatite
  • Aquamarine
  • Aventurine
  • Azotic Topaz
  • Azurite
  • Black Opal
  • Bloodstone
  • Boulder Opal
  • Carnelian
  • Cat's Eye Apatite
  • Cat's Eye Aquamarine
  • Cat's Eye Gemstones
  • Cat's Eye Moonstone
  • Cat's Eye Opal
  • Cat's Eye Scapolite
  • Chalcedony
  • Charoite
  • Chocolate Opal
  • Chrome Diopside
  • Chrysoberyl
  • Chrysoberyl Cat's Eye
  • Chrysocolla
  • Chrysoprase
  • Citrine
  • Color Change Gemstones
  • Color-Change Diaspore
  • Color-Change Fluorite
  • Color-Change Garnet
  • Coral
  • Demantoid Garnet
  • Dendritic Agate
  • Diamond
  • Druzy Amethyst
  • Druzy Azurite
  • Druzy Citrine
  • Druzy Variscite
  • Emerald
  • Enstatite
  • Fire Agate
  • Fire Opal
  • Fluorite
  • Fossil Coral
  • Garnet
  • Golden Beryl
  • Grandidierite
  • Grossularite Garnet
  • Hawk's Eye
  • Hematite
  • Hemimorphite
  • Hemimorphite Druzy
  • Hessonite Garnet
  • Howlite
  • Idocrase
  • Imperial Topaz
  • Iolite
  • Jade Gemstones
  • Jadeite
  • Jasper
  • Kornerupine
  • Kunzite
  • Kyanite
  • Labradorite
  • Lapis Lazuli
  • Larimar
  • Malachite
  • Malaya Garnet
  • Mali Garnet
  • Maw-Sit-Sit
  • Moonstone
  • Morganite
  • Mother Of Pearl
  • Mystic Quartz
  • Mystic Topaz
  • Nuummite
  • Obsidian
  • Onyx
  • Opal
  • Opal Doublet
  • Opal In Matrix
  • Pearl
  • Peridot
  • Pietersite
  • Prehnite
  • Psilomelane Dendrite
  • Pyrite
  • Pyrope Garnet
  • Quartz
  • Quartz Cat's Eye
  • Quartz With Hedenbergite
  • Quartz With Marcasite
  • Rainbow Moonstone
  • Rainbow Pyrite
  • Rhodochrosite
  • Rhodolite Garnet
  • Rhodonite
  • Rose Quartz
  • Rubellite Tourmaline
  • Ruby
  • Ruby In Fuchsite
  • Ruby-Zoisite
  • Rutile Quartz
  • Sapphire
  • Scapolite
  • Scolecite
  • Seraphinite
  • Serpentine
  • Sillimanite
  • Sillimanite Cat's Eye
  • Smithsonite
  • Smoky Quartz
  • Snowflake Obsidian
  • Sodalite
  • Spectrolite
  • Spessartite Garnet
  • Sphalerite
  • Sphene
  • Spinel
  • Star Diopside
  • Star Garnet
  • Star Gemstones
  • Star Moonstone
  • Star Rose Quartz
  • Star Ruby
  • Star Sapphire
  • Strawberry Quartz
  • Sunstone
  • Tanzanite
  • Tiger's Eye
  • Tiger's Eye Matrix
  • Topaz
  • Tourmaline
  • Tsavorite Garnet
  • Turquoise
  • Variscite
  • Zircon
Main Categories
  • New Arrivals
  • Gemstone Lots
  • Calibrated Gemstones
  • Gemstones By Piece
  • Top Grade Gems
  • Matching Pairs
  • Cabochon Gemstones
  • Drilled Gems, Briolettes and Beads
  • Birthstones
  • Gemstone Carvings
  • Fancy Gemstones
  • Star Gemstones
  • Unheated Sapphire
English speaking customer support only

Toll Free - USA & Canada only:
1-800-464-1640

International:
+66-39609697

Save Money
No shipping Fees for Additional Items!
$8.90 Worldwide Shipping

Update Translation
 
Current Value
New Value
GemSelect Gemstones
X Close Window
Colored Gemstones
X Close Window
Colored Gemstones
X Close Window
Colored Gemstones
Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart