Loose Natural Blue Sapphire Gemstones

Colour: what to look for

Colour matters more than anything else in a blue sapphire. Judge it on three things: hue (pure blue, or leaning violet or green), tone (how light or dark) and saturation (how vivid).

• The most sought-after stones are a strong, even blue of medium to medium-dark tone.
• Very dark stones can look almost black in dim light; very light ones look bright but less blue.
• “Royal blue” and “cornflower” are trade descriptions, not grades. Compare the photos and videos of each stone instead.
• Look for even colour across the face of the stone. Visible bands or patches of colour (zoning) lower the value.

Treatments: heated and unheated

Most blue sapphires on the market are heated to improve their colour and clarity. Heating is a long-accepted, permanent treatment. Unheated sapphires with good colour are much rarer and cost more.

• Each stone’s page states its treatment on the Treatment line of its specifications.
• Treatments beyond heating, such as diffusion or fracture filling, change what a stone is worth. If a listing isn’t clear, ask us before you buy.

Measurements: carat versus size

Carat is weight, not size. Sapphire is denser than diamond, so a 1 ct sapphire looks a little smaller than a 1 ct diamond. Compare stones by their measurements instead.

• Use the length × width in millimetres, listed on every stone, to see how big it will look from above.
• Check the depth too: a deep stone carries weight underneath, so it can look smaller than its carat weight suggests.
• If you have a setting already, its millimetre size matters more than the carat weight.

Certification

Selected stones come with an independent IGI report confirming that the stone is natural sapphire and stating any treatment. Where a report is on file, you can open it from the stone’s page. For a stone without one, you can request an IGI certificate from its page before you buy.

Choosing a loose sapphire for a ring

• Sapphire is 9 on the Mohs hardness scale, second only to diamond, so it is well suited to everyday rings, including engagement rings.
• Oval and cushion shapes are popular for rings because they keep colour and weight well. Rounds suit classic solitaire settings.
• Choose the stone first, then have your jeweller make or adjust the setting to its exact measurements.
• For a ring worn every day, a bezel or a setting with sturdy prongs protects the edges of the stone.
• Want more photos or a video in daylight before deciding? Ask us on WhatsApp from any stone’s page.

Read more in our Blue Sapphire Buying Guide and Is Sapphire Good for Engagement Rings?