The Perfect Imperfections: Asterisms

Whilst we are always in search for perfection in gemstones, we also love all things rare and unique. Natural inclusions can bring a whole new character and beauty to a stone. Sami wants to share her favourite types of "imperfectly perfect" gemstones with you in this new series, called The Perfect Imperfections.

What Is An Asterism?

An asterism is a rare, cloudy-opalescent star shaped pattern that can be displayed in a variety of crystals, including sapphire, ruby, moonstone, garnet, spinel, topaz, diopside and emerald. The asterism usually has six points, however they can range from 4 to 12 points, with 12 being the most rare and valuable.

This optical illusion is formed from dense rutile inclusions that have a higher refraction index than the actual gemstone, causing light to be reflected into a starburst formation. The magical properties of this phenomenon allow the star to "dance" when the gemstone is rotated. 

Types Of Asterisms

There are two types of asterism, which are an Epiasterism and a Diasterism.

An Epiasterism is where light is reflected from parallel inclusions within the gemstone, most commonly occurring is sapphires.

A Diasterism is when a gemstone is back-lit so that light can travel through the crystal and is most commonly seen in rose quartz.

A Jeweller's Tips

A gemstone that displays an asterism should not be cut, but instead polished into a cabochon shape. The value of an asterism gemstone depends on the clarity and even light distribution, in addition to the number of points displayed. Burmese and Sri Lankan Rubies and Sapphires, and 12-point asterism gemstones have the greatest value for those who are looking to invest. 

Mythology

Legend has it that asterisms were formed when a sunbeam fell in love with a beautiful star.

Famous Asterism Gemstones

The Star of India is a blue sapphire that weighs an impressive 563 carats and currently resides at the Natural History Museum, New York City.

The Rosser Reeves is a Sri Lankan ruby that weighs 138.7 carats and is exhibited at the Smithsonian Institute, Washington, D.C.

This fascinating imperfection has become treasured around the world and will provide a spark of magic to your gemstone collection.