Sapphire Gemstone Guide: Colours, Australian Origins and Engagement Rings

What is a sapphire gemstone?

A sapphire is a gem-quality crystal of corundum, the mineral form of aluminium oxide (Al₂O₃). Pure corundum is colourless. Tiny amounts of other elements trapped in the crystal as it grows, such as iron, titanium, chromium and vanadium, give sapphire its colours. When chromium turns corundum red, the stone is called a ruby instead; our guide to how ruby and sapphire differ explains where the line sits between the two.

Corundum crystallises in the trigonal system, usually as barrel-shaped or tabular crystals. For a gemmologist, sapphire has a distinctive set of numbers that help identify it on the bench:

• Hardness: 9 on the Mohs scale (a scale of scratch resistance from 1 to 10).
• Refractive index: 1.762–1.770, with birefringence (the gap between its two readings) of 0.008–0.010.
• Specific gravity: about 3.95–4.03, so it is heavier than diamond (3.52) for the same size.
• Pleochroism: it shows two slightly different colours from different directions; a blue sapphire often looks violet-blue one way and greenish-blue the other.
• Lustre: vitreous to sub-adamantine (bright and glassy, just below diamond's sharp shine).
• Dispersion: about 0.018, much lower than diamond's 0.044, so sapphire shows colour rather than rainbow fire.

Sapphire sits alongside emerald, spinel, tourmaline and the rest of our coloured gemstones hub. If any term here is new, the GemTrove jewellery glossary defines it in plain English.

What colours do sapphires come in?

Blue is the colour most people picture, but sapphire comes in almost every hue. In the trade, any colour other than blue is called a fancy sapphire. Each colour has a different chemical cause, which also affects how it behaves under different lighting.

Each fancy colour has its own guide: green sapphire, purple sapphire, orange sapphire, the rare pinkish-orange padparadscha, stones that shift hue in colour-change sapphire and the colourless white sapphire often chosen as a diamond alternative.

Colour drives value more than anything else. Gemmologists judge it in three parts: hue (the basic colour, such as blue or violet-blue), tone (how light or dark) and saturation (how intense, versus greyish or brownish). A blue that is too dark looks almost black indoors; one too light looks washed out. If you are torn between blue and blue-green, see how teal compares with blue on the hand.

Where do Australian sapphires come from?

Australia's sapphires come mainly from two basalt-related fields: the New England region of northern New South Wales, around Inverell and Glen Innes, and the Central Queensland gemfields, around Anakie, Sapphire and Rubyvale. For several decades in the later twentieth century Australia was one of the world's major producers, and much of its rough was cut overseas, so many Australian stones have been sold without their origin being named.

Because they form in iron-rich conditions, Australian sapphires tend to be deep, inky blue, along with teal, green, yellow and two-toned stones. Those two-toned crystals, showing blue, green and yellow zones in one stone, are known as parti sapphires and have become a signature of Australian material. Blue-green stones are also popular, which is why teal sapphire rings are so often Australian.

Origin is an opinion, not a certainty: labs base it on inclusions, trace-element chemistry and spectroscopy, and two labs can occasionally disagree. Our guide to what Ceylon origin really means explains how origin reports work. For locally sourced stones set into rings, see Australian sapphire engagement rings.

Is sapphire hard enough for an engagement ring?

Yes. Wearability depends on two separate properties. Hardness is resistance to scratching; at 9, sapphire is scratched only by diamond and a handful of other materials, and everyday dust (mostly quartz, at 7) cannot scratch it. Toughness is resistance to chipping and breaking. Sapphire has no cleavage (a natural plane along which a crystal splits), so its toughness is rated excellent, better in practice than many people expect.

Sapphire can still chip if it takes a hard knock on a sharp edge, and some stones have parting (weak planes caused by twinning) that a skilled setter will check for. Our comparison of diamond vs sapphire for an engagement ring covers sparkle and price as well, and emerald vs sapphire shows why emerald needs more protection.

Are sapphires heat-treated?

Most are. Heating sapphire to high temperatures, often 1,200–1,800°C, can deepen or lighten colour and dissolve fine rutile needles called silk. It is a long-established, permanent treatment and is widely accepted in the trade, but it must be disclosed. An unheated stone of the same quality usually costs considerably more.

Heat treatment is detected under the microscope from altered inclusions, such as broken-up silk and disc-shaped stress fractures, and by laboratory spectroscopy. For a significant stone, ask for an independent report that states whether there is evidence of heating or other treatment.

What is a synthetic sapphire and how can you tell?

A synthetic sapphire, also called a lab-created sapphire, has the same chemistry, hardness and optical properties as natural sapphire but is grown in a laboratory. It is not an imitation: it is real corundum, just not mined. Imitations are different materials that only look similar, such as blue glass, synthetic spinel, iolite or a doublet (a thin slice of natural sapphire glued onto a synthetic base).

Lab-created sapphire has been made since the early twentieth century. The main methods are flame fusion (the Verneuil process, where powder is melted through a flame and builds up a crystal), Czochralski pulling (drawing a crystal from a melt, also used for industrial and laser crystals) and slower flux and hydrothermal growth, which produce more natural-looking crystals.

Telling the two apart often needs magnification: a gemmologist looks for curved striae (growth lines) and round bubbles that point to flame fusion, against the straight, hexagonal colour banding of natural growth. Flux and hydrothermal stones can be harder and may need a laboratory. Both are legitimate choices, as long as you know which one you are buying.

How much is a sapphire gemstone worth in Australia?

Price per carat rises sharply with colour quality, size, treatment status and, for top stones, a documented origin. The ranges below are rough guides for loose stones in AUD; individual stones vary widely.

Clarity matters too. Sapphire is a Type II coloured stone, meaning it usually has some inclusions, so the aim is an eye-clean stone, not a flawless one. Fine silk can even soften the colour pleasantly. Cut matters for appearance: many sapphires are cut deep to keep weight, which makes them look smaller, or shallow, which creates a window (a washed-out patch in the centre).

Size also differs from diamond. Because sapphire is denser, a 1 carat round sapphire measures about 6.0–6.2 mm across, against about 6.4–6.5 mm for a 1 carat round diamond, so compare millimetres rather than carats.

Are sapphire gemstones good for engagement rings?

Sapphire is one of the most practical coloured stones for a ring worn every day, which is why so many people searching for sapphire engagement rings in Australia end up choosing one. Medium to medium-dark blues read clearly from across a room; teal, green and parti stones suit people who want something less traditional. Lighter colours and white sapphire show dirt sooner than diamond, so they need regular cleaning to stay bright.

Settings work much as they do for diamond. Four or six claws show the most colour; a bezel (a metal rim around the stone) protects the edge and suits active hands; a diamond halo brightens darker stones. White metals cool and sharpen blue, while yellow gold warms teal and green. See our sapphire engagement rings in Melbourne for examples of each style.

How to choose a sapphire gemstone: step by step

1. Decide on colour first. Pick the hue you love, then look for a medium to medium-dark tone with strong saturation.
2. Ask natural or lab-created. Make sure the stone is clearly described, and if natural, whether it is heated or otherwise treated.
3. Check it in two lights. Look in daylight and under warm indoor light; note any darkening or colour change.
4. Look for eye-clean clarity and a good cut. Turn the stone face-up and check for windowing or dark, dead areas.
5. Compare millimetres, not carats. Sapphire is denser than diamond, so measure the face-up size.
6. Get a report for a significant stone. For unheated, fine or padparadscha stones, ask for an independent lab report covering treatment and, if important to you, origin.
7. Plan the setting. Match the metal to the colour and choose claws or a bezel that suit how you wear jewellery.

Clean sapphire with warm soapy water and a soft brush. Heated and untreated stones usually tolerate ultrasonic cleaning, but fracture-filled or glass-filled stones should never go in an ultrasonic or steamer.