ENCYCLOPEDIA · SKYJEMS

Ceylon Star Sapphire — Unheated

Key concepts

ceylon star sapphire, star sapphire, asterism, sri lanka star sapphire, unheated star sapphire

A star sapphire carries a six-rayed figure that glides across the dome as the stone moves. The effect is called asterism, and it comes from needle-like rutile inclusions arranged along the crystal's own structure — the same silk that, in a faceted sapphire, would be counted a flaw. In a cabochon it is the entire point.

Sri Lanka has been the classic source for centuries, and its stars tend to run blue, sometimes with a grey or violet cast.

What separates a good star from an ordinary one

Four things, in roughly this order. The star should be straight, complete and centred, with all six legs present rather than fading out. It should be sharp rather than diffuse. The body colour should be a clean blue rather than a muddy grey. And the dome should be cut high enough to gather the star without turning the stone into a marble.

A star that only appears under a single hard light and vanishes in a room is a weak star, whatever the size of the stone.

Treatment — the questions to ask

Sapphire is routinely heated, and star sapphire carries two concerns of its own, both worth naming rather than asking about in general. Diffusion treatment can be used to create or strengthen an asterism. And synthetic star sapphire is common — laboratory-grown corundum with a diffusion-induced star is well documented, and it is the likelier trap at the affordable end of the market. Ask whether a star is natural in origin, not merely whether the stone is a sapphire. Our Ceylon star sapphires are unheated, and treatment is confirmed stone by stone rather than assumed. Review each listing and its documentation for the individual gem.

Reading the lab report

A report on star sapphire states species = corundum, variety = sapphire, records the phenomenon, and records treatment. GIA is the laboratory we lead with, and where a stone carries a GIA report we list its number on the product page. The wider selection is assessed in-house.

What to look at

(1) is the star complete, centred and straight; (2) is it sharp under ordinary room light, not just a torch; (3) body colour, clean rather than grey; (4) dome proportion; (5) treatment and origin, asked specifically — including diffusion and whether the stone is natural.

Skyjems inventory snapshot

Browse sapphire at /collections/sapphire. Skyjems' selection changes as stones are added or sold; review each current listing for its own documentation.

Private viewings

Contact Skyjems at +1-416-366-3335 or visit Skyjems' private-viewing page.

Sources and further reading

• Sapphire Quality Factors
• Gems & Gemology, Summer 2015 — synthetic sapphire with a diffusion-induced star