Asterism: when the star (inclusions) align

One could argue that all gemstones are phenomenal; after all, what else on our planet is as beautiful and intriguing as a jewel?

But true ‘phenomenal’ stones are those gems that go above and beyond with unique and stunning attributes. Opals with play-of-color, alexandrities with color changing abilities, and cat’s-eye stones displaying chatoyancy, to name a few.

In terms of magical presence, however, gemstones that display asterism might be the winners in the phenomenal category.

Asterism is the term given to gemstones that display a ‘star” pattern. These stones are almost always cut as cabochons so that the effect can be readily seen. The star can have four, six, eight or even twelve rays.

~Sample image of blue and black star sapphires

Asterism is caused by microscopic, intersecting needle inclusions, the most common of which are rutile. These needles must be oriented at just the right angles to produce a star pattern when light enters the stone and then reflects off the inclusions.

As you can imagine, such an effect is rare and absolutely enchanting.

~Photomicrograph of "silk" inclusions in a sapphire, x30 magnification (Photo by Isabelle Corvin)

Gems that can showcase stars are sapphires and rubies, as well as rose quartz, spinel and garnet. A few other, extremely rare minerals have also been found with asterism on occasion.

Star sapphires are likely the most well known of the bunch, with the most famous likely being the Star of India, a 563.35ct star sapphire that many estimate to be around two billion years old.

The most common use of the word asterism is used in astronomy to refer to a group of stars that are smaller than a constellation.

In fact, the Big Dipper is actually an asterism, as it’s part of the larger constellation Ursa Major (the Great Bear).

The word ‘asterism’ comes from the Greek root word of ‘asterismos’, believed to literally mean “marking with stars”.

With such an unusual and magical appearance, its’ no wonder that whispered myths about gemstones that display asterism can be found here and there.

Even now, with our understanding of how these star patterns come to be, the chance that the inclusions are the right kind, in the right place, at the right angles, makes this type of phenomena rare when naturally occurring.

Some of the oldest stories come from Ceylon, where star sapphires were believed to be wards against witchcraft, hexes and curses, as well as guards against the ‘evil eye’.

In the early Catholic church, the intersecting bands of six-rayed stars were said to represent faith, hope and charity.

Other tales speak of how a gemstone with a star pattern could act as a compass, not only for finding north but also in a more whimsical sense of finding direction in life. This belief of star stones being a guiding stone persists today in modern crystal symbolism.

Arab legend states that the star sapphire would give the wearer the ability to speak and understand the language of the genii.

Some stories even claim that part of Helen of Troy’s charm and beauty was due to her supposedly owning a large star sapphire.


Gemstones that display asterism are believed to have more energy to them then the ‘normal’ versions of each stone, making any healing abilities associated with the gems more powerful.

Laboratory grown versions of star stones, especially ruby and sapphire, are common and can mimic the effect perfectly. While not as rare as the natural varieties, they are lovely and still showcase that incredibly unique pattern.

Gemstones with asterisms are the perfect showcase of why inclusions aren’t always a detriment to a jewel’s beauty. In fact, they can enhance it.

To think that something can be found on earth that mirrors the stars above is just one more reason that gemstones and jewelry continue to fascinate and entice humans to this very day.

If anyone is looking for a little magic in their life, a gemstone with asterism might just be a good fit.

~Blog written by Isabelle Corvin, staff gemologist and merchandising manager