Question 1

What causes the star in a star ruby?

Accepted Answer

Asterism is caused by tiny needle-like rutile inclusions, called silk, oriented in three directions at 60 degrees to one another. When the stone is cut as a cabochon with the correct orientation, reflected light forms six rays. The star is seen best under a single point of light, such as sunlight or a spotlight, and looks softer in diffuse light.

Question 2

How can I tell if a star ruby is natural?

Accepted Answer

Synthetic star rubies often show an unusually sharp, perfect star, very even colour and curved growth lines under magnification, while natural stones show straight colour zoning and less uniform silk. These are only indications, however. A laboratory report is the reliable way to confirm a natural ruby with natural asterism and to disclose any treatment.

Question 3

Are star rubies heat treated?

Accepted Answer

Many are not, because strong heating dissolves the rutile silk that creates the star. Star rubies can, however, be subject to other treatments, including diffusion to create or strengthen asterism and fracture filling or dyeing in lower grades. A laboratory report should state the treatment status of any significant stone before purchase.

Question 4

How should a star ruby be set?

Accepted Answer

Choose a setting that leaves the dome fully exposed and lets light reach it from above, so the star can move freely. Bezel and low-profile prong settings both work well. Because cabochons often have heavy bases, check the depth before designing the mounting. Ruby has a hardness of 9, but heavily included stones can be more vulnerable to hard knocks.

Star Rubies