STAR SAPPHIRE GUIDE

Asterism in sapphires is caused by dense concentrations of microscopic rutile (titanium dioxide) needles aligned along the crystallographic axes of the corundum crystal. Sapphire has three crystallographic planes at 60° angles to each other. When rutile needles align along all three planes simultaneously, they create three sets of parallel reflectors that, under a single light source, reflect light into six rays — producing the characteristic six-rayed star.

The stone must be cut as a cabochon (domed, with flat base) to display the star. The dome must be shaped and oriented correctly relative to the crystal's c-axis — if the dome is off-center, the star will be displaced from the apex or its rays will be uneven.

Some corundum crystals contain rutile needles in six directions rather than three, producing a rare twelve-rayed star. These "twelve-rayed" or "double star" sapphires are extraordinarily rare and command significant premiums.

The two most commercially significant star sapphire varieties are blue star and black star, which differ dramatically in character, origin, and price:

Blue star sapphires display a blue, blue-grey, or grey-blue body color with a white or silver star. The finest examples come from Ceylon and Burma — stones with a strong, vivid blue body color and a crisp, centered silver star. These are the traditional collector's star sapphire and command the highest prices.

Black star sapphires are typically opaque dark blue-green to nearly black stones that display a gold or silvery star against the dark body. The most famous source is Chanthaburi, Thailand. Black star sapphires are significantly less expensive than blue stars and appeal to buyers seeking dramatic visual effect at lower price points.

Ceylon produces the benchmark for investment-grade blue star sapphires. The Ratnapura and Elahera regions of Sri Lanka have yielded some of the world's finest examples — stones with strong blue color and sharp, well-centered stars in sizes reaching hundreds of carats.

Burma's Mogok Valley produces blue star sapphires that, like their faceted counterparts, command premiums for origin. Burma star sapphires often display a slightly warmer blue tone compared to Ceylon.

India (Orissa state) has historically been a source of star sapphires, including some famous historical specimens, but production quality is variable. Myanmar (Burma) star sapphires are less commonly encountered than Ceylon material.

The star sapphire market has significant issues with synthetic and treated material:

Synthetic star sapphires (Verneuil process) are produced in vast quantities and sold at low prices. They display extremely sharp, perfect stars — often suspiciously perfect. Natural stars have slight irregularities in ray width and sharpness; synthetic stars look machine-perfect.

Diffusion-treated stars are natural sapphires that have had a star induced or enhanced through surface diffusion of titanium. The star is a superficial phenomenon — it may disappear if the stone is re-polished.

For investment purposes, GRS or Gübelin certification is essential to confirm natural asterism, natural color, and origin. Never purchase a star sapphire at investment prices without laboratory confirmation.