Learn about Australian sapphires
Sapphire buying gets easier once you know what the words mean. This page covers the terms that come up most often when people are looking at Australian stones — parti, teal, unheated, carat versus millimetres, cut quality and care. It is the plain version. Naseeb digs and cuts these stones himself on the Queensland gemfields around Rubyvale, and most of what follows comes from what actually turns up in the wash and on the wheel.
Parti sapphires
A parti sapphire is a single crystal showing more than one colour at once. The name is short for particoloured. The usual combination in Australian material is blue, green and gold, though you will see blue-and-yellow splits, green-and-gold, and stones where three or four zones run through the one gem.
How the colours get there
Sapphire is corundum, and pure corundum is colourless. All the colour comes from tiny amounts of other elements caught in the crystal as it grew. Iron and titanium together give blue. Iron on its own gives the yellows and golds. Crystals do not grow all at once — they build up in layers, and if the chemistry of the fluid around them changes partway through, the next layer comes out a different colour. Those layers are what you are looking at.
This is why the cutter matters so much with parti. The same rough crystal can be oriented to show a clean two-colour split, a soft blend, or a burst of colour from the centre. Turn it ninety degrees and you get a completely different stone.
Why Australia
Eastern Australian sapphires come up through basalt volcanism, and that geology produces iron-rich stones. Iron is what puts the gold and green in the mix. Many of the world’s other famous sapphire sources are metamorphic and low in iron, which is why they produce beautiful blues but very little parti. Queensland and New South Wales are the main commercial source of parti sapphire.
What to look for
- Judge the stone face-up, the way it will sit in a ring. Colour zones that look dramatic from the side often disappear from the top.
- Look for colours that stay distinct. Muddy transitions where blue and yellow blur into a grey-green band are less interesting than a clean boundary.
- Check it under more than one light. Daylight, warm indoor light and shade all pull different amounts of blue and gold forward.
- Ask for video. A still photograph is one lighting angle. Parti stones change constantly as they move, and that movement is most of the appeal.
- Accept that no two are alike. There is no standard parti and no grading scale for it. Buy the individual stone in front of you.
Teal sapphires
Teal describes a sapphire sitting somewhere on the blue-green spectrum. It runs from blue with a green cast, through an even split, to green with a blue cast. It is a trade term rather than a gemological one — there is no agreed line where blue stops and teal begins.
Teal stones have become one of the most-requested options for engagement rings over the past decade. Part of that is the general move away from colourless diamonds. Part of it is that teal is unusually easy to wear — it works with white metals and yellow gold, and it does not read as a statement colour the way a strong blue or a pink does.
The difference from parti is straightforward. A teal sapphire reads as one colour, even though that colour is a blend. A parti sapphire shows separate colours in separate parts of the stone. Plenty of Australian gems sit on the boundary.
Teal stones often shift noticeably between light sources, leaning greener in daylight and warmer or greyer under incandescent bulbs. That is normal and not a fault.
No heat and unheated — what treatment actually means
Heat treatment is standard practice across the world sapphire trade and has been for a very long time. The stone is taken to high temperature, which can deepen or lighten colour and dissolve the fine internal silk that makes some stones look hazy. The change is permanent and stable. A heated sapphire is still a natural sapphire, dug out of the ground, and it wears exactly the same as an unheated one. It is not a fake and it is not damaged goods. Probably the majority of sapphires sold worldwide have been heated.
Unheated stones command a premium because they are less common — the gem came out of the ground looking the way it looks. How large that premium is varies enormously.
With Australian parti and teal material there is a practical reason a lot of it is left alone: heat tends to even out colour, and evening out the colour is exactly what you do not want when the colour zoning is the point.
The rule that matters is disclosure. Any treatment should be stated plainly by the seller, every time, whether it is heat or something else entirely such as lattice diffusion or fracture filling — those are different processes with different implications, and they are not the same thing as ordinary heating.
Carat versus millimetres
Carat is a unit of weight, not size. One carat is 0.2 grams. This trips people up constantly, because two stones of identical carat weight can look very different on the hand.
- Density. Sapphire is denser than diamond. A one carat round diamond measures roughly 6.5 mm across; a one carat round sapphire is closer to 6.0 mm.
- Cut depth. Weight hidden below the girdle does nothing for face-up appearance. A deep stone can look a full size smaller than a shallower stone of the same weight.
- Shape. Elongated shapes — ovals, pears, marquise, elongated cushions — spread more across the finger than rounds of the same weight.
So ask for the millimetre dimensions: length, width and depth. Then measure those against a ring you already own. Millimetres tell you what the stone will look like. Carat tells you what it weighs.
How to read a cut
You do not need a loupe or a grading report to tell a good cut from a poor one. You need to know three words.
Light return
Hold the stone face-up under ordinary room light. A well-cut gem is bright right out to the edges, with light bouncing back at you from across the whole surface.
Windowing
A window is a see-through area, usually in the centre, where light passes straight through the stone instead of reflecting back. It happens when the pavilion is cut too shallow. Lay the stone over a line of printed text — if you can read the words through it, that is a window. Small ones are common and tolerable. A big one drains the colour.
Extinction
Extinction is the opposite problem — dark areas where no light comes back. A bit is fine and actually desirable, because the contrast between bright and dark is what makes a stone sparkle. Too much and the gem looks dead.
Beyond those three, look at symmetry, and look at video rather than stills wherever you can. A still image can be lit to hide a window completely.
Caring for your sapphire
Sapphire sits at 9 on the Mohs hardness scale, behind only diamond among the stones you would normally set in jewellery. It handles daily wear better than almost anything else.
Hardness is about scratch resistance though, not invulnerability. A sharp knock on an exposed corner can still chip a stone.
- Cleaning. Warm water, a drop of dishwashing liquid, a soft toothbrush around the back of the setting, then rinse and dry with a lint-free cloth.
- Ultrasonic and steam. Usually fine for a clean, untreated sapphire in a sound setting — but not if the stone has significant fractures. Ask your jeweller.
- Take it off for gardening, gym work and household cleaning. Chlorine will not hurt the sapphire, but it will attack the alloys in gold settings over time.
- Storage. Store rings separately, in a pouch or lined box. Sapphire will scratch nearly everything else you own.
- Setting checks. Have the claws or bezel checked every six to twelve months if you wear the piece daily, and immediately if the stone rattles when you tap the ring near your ear.
Where to go next
If you have a stone in mind and want it built into something, the Gem Design Studio walks through the ring design process with us.
If you are still looking, the loose stones are at gemstones. Every one is a single piece, so take your time with the dimensions and the video before you decide.