Sapphire is the gem variety of the mineral corundum, an aluminium oxide. It rates 9 on the Mohs scale, second only to diamond among gems, which makes it one of the best coloured stones for jewelry worn every day.
Many colours
Blue is the most famous, coloured by traces of iron and titanium. But corundum occurs in almost every colour: pink, yellow, orange, green, purple and colourless. Red corundum is called ruby. A pinkish-orange variety is known as padparadscha. Some sapphires show a star when cut as cabochons, caused by fine needle-like inclusions.
How quality is judged
| Factor | What to look for |
|---|---|
| Colour | The most important factor: hue, tone and saturation. For blue, strong, even colour that is neither too light nor too dark |
| Clarity | Inclusions are common; they should not detract from beauty or durability |
| Cut | Even colour and brightness across the face of the stone |
| Carat | Fine sapphires in larger sizes are rare |
Origin
Sapphires are mined in several countries, including Sri Lanka, Madagascar, Myanmar, Australia and Thailand. Some origins carry historic prestige, which can affect price. Origin can only be established by specialised laboratory reports, and not for every stone.
Treatments
- Heating: common and widely accepted; results are generally stable.
- Diffusion: adds colour from outside the stone; must be disclosed.
- Fracture or glass filling: improves apparent clarity; must be disclosed and needs gentle care.
DORVETTI always discloses known treatments.
Laboratory-grown sapphire
Corundum has been grown in laboratories since the early twentieth century, notably by the flame-fusion process developed by Auguste Verneuil. A laboratory-grown sapphire is sapphire, and must be described as laboratory-grown. Read Natural vs lab-grown gemstones.
Care
Warm soapy water and a soft brush are ideal. Avoid ultrasonic and steam cleaning for filled or diffusion-treated stones.
Sapphire and other blue gems
| Gem | Hardness (Mohs) | Notes |
|---|---|---|
| Sapphire | 9 | The most durable blue gem after blue diamond |
| Spinel | 7.5–8 | Durable; can be a vivid blue |
| Blue topaz | 8 | Usually treated; prone to cleavage |
| Tanzanite | 6–7 | Violet-blue; needs protection in rings |
| Aquamarine | 7.5–8 | Light, sea-blue colour |
Setting a sapphire
Sapphire's hardness suits every setting. Its colour interacts with the metal: white metals make blues look cooler and crisper; yellow gold warms them. Diamonds around a sapphire, in a halo or three-stone design, emphasise its colour.
What affects price
- Colour quality, above all.
- Size: fine sapphires above a few carats are rare.
- Treatment: untreated stones of fine quality are rarer.
- Origin, for stones with laboratory origin reports.
- Natural or laboratory-grown.
Documentation
For significant sapphires, ask for a report from an independent laboratory stating the species, whether the stone is natural or laboratory-grown, and any treatment detected. Origin opinions are a separate service and not available for every stone.
Sources: Gemological Institute of America (gia.edu), gem encyclopedia; US Federal Trade Commission, Guides for the Jewelry, Precious Metals, and Pewter Industries, 16 CFR Part 23.
Frequently asked questions
Is a heated sapphire less valuable?
Heating is common and widely accepted, and its results are generally stable. Unheated sapphires of comparable quality are rarer and usually command higher prices. Treatment should always be disclosed.
Is a lab-grown sapphire real sapphire?
Yes. It has the same composition and structure as natural sapphire, and must be identified as laboratory-grown.
Are sapphires only blue?
No. Sapphires occur in almost every colour; only red corundum is called ruby instead.
Is sapphire good for an engagement ring?
Yes. At 9 on the Mohs scale it is one of the most durable gems for daily wear.
