The short answer: a star sapphire shows a star shaped glow across a smooth, domed surface, caused by tiny needle like inclusions that reflect light, and the finest ones have a sharp, centred star and good colour. Choose a stone where the star is clear and the body colour pleases you.
Star sapphires are cut as cabochons, which are smooth domes, instead of faceted. The star, called asterism, moves across the stone as the light changes.
How the star forms
Tiny needle like crystals inside the stone, often rutile, line up in three directions. When light hits the dome, it reflects from these needles and forms a six rayed star.
What to look for
- Sharp star: distinct lines rather than a blurry glow.
- Centred star: sitting in the middle of the dome.
- Complete rays: all six lines visible and even.
- Body colour: a colour you like, as star sapphires come in blue, grey, pink and more.
Balancing star and colour
The silk that creates the star also affects how the stone looks. Plenty of silk gives a strong star but can make the body colour look milky or grey. Less silk can give richer colour but a fainter star. The finest stones manage both, a vivid colour and a sharp star, which is why they are rare. Decide which matters more to you, and we look for a stone that strikes your balance.
Light matters
A star shows best under a single bright light, such as a lamp or sunlight. In soft or diffused light it can be faint. We show stones on video with a point light so you can judge.
Cut and shape
Cabochons are usually round or oval. The height of the dome affects the star, and a good cutter positions the star carefully. A dome that is too flat can weaken the star, and one that is too tall can look bulky in a ring.
Settings
A bezel or a protective claw setting suits a cabochon. A simple band lets the star take attention. Rose gold and yellow gold suit warmer stones, and white metals suit cool blues. A star sapphire also suits a signet style ring, where the dome sits flush in a broad face.
Star sapphire or star ruby?
Star rubies show the same effect in a red stone. Both are corundum, the same mineral family, and both are very hard. Star rubies tend to be rarer and priced accordingly, and star sapphires offer a wider range of colours. See our guide to ruby settings if red appeals to you.
Everyday wear
Star sapphires are durable, as sapphire is very hard. The domed surface can show scratches over time, and a light polish can refresh it. See our guide to cleavage and chips for how to protect any stone from knocks.
Natural or lab grown
Star sapphires also exist as lab grown stones, and the star can be created during growth. Lab grown stars are often very sharp and evenly placed, while natural stars tend to be softer and more individual. We describe each stone clearly. See lab grown sapphire, ruby and emerald vs natural.
How to choose
- Look for a sharp, centred star.
- Choose a body colour you love.
- See it in point light.
- Pick a secure setting.
See best settings for sapphire and celestial engagement rings. Nothing is made until you approve the design in writing, and our standard making time is 5 to 6 weeks, which can vary with your location and how busy we are. Pieces start from £600.
Frequently asked questions
Is a star sapphire a real sapphire? Yes, with a special optical effect.
Does the star fade? No, it is part of the stone.
Is it good for an engagement ring? Yes, with a secure setting.
Why is it not faceted? The smooth dome is what lets the star show.
Can I order from overseas? Yes, by video consultation, with insured, tracked FedEx delivery.