Why Are Sapphires Blue ? Here’s How They Get That Perfect Blue

Sapphires are among the oldest and most impressive gemstones known to man. These deep blue gems have been fought over, cried over, and one of them rests at the bottom of the ocean in the gut-wrenching Titanic story (at least in the movie). Because of their royal blue color sapphires are some of the most recognizable gemstones in history, as few others manage such a deep, velvety blue.

But how do sapphires get their intense blue color ? Do they come out of the earth looking impressive, or is there something more to them ? Today we’re looking at what makes sapphires such a beautiful shade of blue, and what other options you have for a deep blue gemstone if you can’t have a sapphire.

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Why are sapphires blue ?

Sapphires are a type of corundum and they owe their blue color to trace amounts of iron and titanium. The more titanium in the sapphire the more vivid the color, and the more iron the darker the color. Very few sapphires are mined with a perfect blue color, as most come out a cloudy blue, sometimes very dark and sometimes nearly white.

Sapphire heat treatment

To improve that blue color and remove any impurities sapphires, almost all sapphires are heat-treated. This means they are heated at temperatures ranging from 800 C t0 1800 C for several hours or more, to get a better color. This treatment can have very dramatic effect, increasing the color saturation and improving clarity.

However because very few natural (untreated) sapphires are eye-clean, a perfectly clear sapphire is almost always a sign of heat treatment. These gemstones are still desirable, but not as much as one that is blue and clear naturally.

Fancy colored sapphires are rare

Despite the association with intense inky blue, sapphires come in a variety of colors, though blue is the preferred color. These are called fancy sapphires, the same way colored diamonds are called fancy diamonds. You’ll find fancy sapphires much harder to get a hold of, as they’re rarer than blue ones. Here are a few examples.

Red sapphires are actually rubies, and they owe their color to chromium in their chemical makeup.

Pink sapphires owe their color to iron, titanium and a bit of chromium in their makeup. These can be classed either as a pink sapphire or as a pink ruby, depending on who you ask.

Padparadscha sapphires have a bit of chromium and iron in their mix, as they end up with a beautiful salmon or coral color. Sometimes they lean more towards pink, sometimes more towards orange. Yellow sapphires have even smaller amounts of just iron.

Read also: Sapphire VS Aquamarine

Green sapphires have small amounts of iron, with much smaller amounts of titanium. These are easy to tell apart from emeralds because they’re a lighter, slightly yellowish green compared to emerald’s deep, darker green.

White sapphire is very rare, because it means it has no trace amounts of other elements, which is very difficult to obtain naturally. Corundum is actually colorless.

Particolored or bicolored sapphires are possibly the rarest kind of sapphires out there. They look like two different colors fused together, and can come in very different combinations, such as yellow-blue, green-purple, green-blue, and so on. The best ones have a clear distinction between the colors and are very clear.

What color sapphires are the most expensive ?

The most desirable and most expensive color sapphire is a deep royal blue with no purple or green flashes. It must be perfectly clear, with no inclusions, and it must not be heat-treated at all. You can get these for anywhere between $1500 and $10k per carat, depending on the cut quality and the geographic origin of the sapphire.

A lab-grown sapphire will easily achieve clarity and color, but will still be priced much cheaper than a stone that is natural but heat-treated. All lab-grown gemstones are cheaper, simply because they’re not natural gemstones, even if they look like the real thing.

Keep in mind that sapphires are very dense and thus heavier than they look. Carats measure weight, not size, so a 1 carat sapphire will weigh the same as a 1 carat diamond, but will look smaller.

Why do some sapphires have a star ?

Sapphires are prone to inclusions, which are small particles of a different material within the sapphire. Sometimes the inclusions are simply tiny fractures. In the case of star sapphires those inclusions are usually rutile (titanium dioxide), and they are tiny, needle-like, and rest just below the surface of the sapphire, in various layers.

These sapphires are prized for their star (called asterism), and are often cut into cabochons, and the star usually shows up near the top of the dome. Because of the way the inclusions are laid into the sapphire, as the light hits the gemstone a star shape appears, with 4,5,6 arms depending on each gemstone.

Unfortunately the stars disappear or at least fade significantly if the sapphire is even heat-treated. Intense, long-term heat dissolves the rutile into the rest of the sapphire, providing a more intense blue color but it can no longer show an asterism.

How to tell if a blue star sapphire is real

You may see blue star sapphires for sale. Not all of them are real, especially since cabochons are easy to make from acryl or plastic. Here’s how to figure out if yours is real.

The star should be imperfect. This means each arm should not be perfectly straight, but instead slightly wavy, some parts brighter and some darker, one side may even be slightly shorter. The point is that these stars cannot be truly perfect because the stone is naturally not arranged this way.

Shine a light on the gemstone. The star should only be visible when held to a single bright light, like direct sunlight. As you move the stone in your hand, the star should follow the light. If you turn the stone and the star is less visible it’s most likely a fake. A true star sapphire’s silk is all over the sapphire and within it, meaning it will show whenever and wherever.

And finally, a perfectly blue sapphire with an asterism is nearly impossible. It would have to be amazingly expensive. A star sapphire is always a bit cloudy or hazy, precisely due to the millions of rutile needles that give it a whitish cast.

Sapphire gemstone alternative (deep blue)

If you’re ever in need of a deep blue gemstone and can’t afford a sapphire, or don’t want to use a sapphire, there are a few other options you can choose from. While no other stone is as deeply and richly blue as sapphire, some do come close.

This list focuses on deep blue stones, not light blue ones and the main care was to find gemstones that could be faceted and used in jewelry like sapphire. Take your pick.


Iolite is a type of cordierite, and it’s called so because it’s derived from the Greek word for violet. So this stone resembles sapphires that lean more towards indigo, rather than royal blue. Still, their overall color is very deep and fairly dark, without appearing black. You may also use this in place of black sapphire, which itself is not pure black but instead a very, very dark midnight blue.

It is not the strongest stone, scoring a 7-7.5 on the Mohs hardness scale. However it can still be used in jewelry, as long as it’s not on a bracelet. If you put it on a ring it needs a bezel setting to be sure it’s kept safe. Other jewelry pieces like pendants or earrings may use a prong setting. 


This gemstone is only found in Tanzania, hence the name. It’s actually a type of zoisite, and it comes in a blue-violet shade. Compared to iolite, it leans more towards blue. You may also find tanzanite that is almost completely blue, but the slight purple tint may please some people.

Like sapphire, tanzanite may be heat-treated to produce a better color. When mined tanzanite displays three colors – brown, blue, purple. After its heat treatment, it loses the brown and intensifies the blue and purple, similar to sapphire.

Tanzanite scores a 6.5 on the Mohs scale, so you need to be extra careful with this gemstone. Choose a protective setting, and you may even surround it with a halo.

Blue spinel

Spinel is a lesser known gem but it’s fairly old. It comes in many colors and for a very long time red spinels were confused for rubies. There are blue spinels, and they range from light icy blue to deep blue to blue-green to grey and nearly black (within the blue range).

This means you can easily find a perfectly blue spinel to use in place of sapphire, if that is what you’re going with. Spinel is a 7.5-8 on the Mohs scale, so it’s reasonably hard and can be worn everyday as long as you take care to shield it from shocks.


This gemstone has actually become the California state gemstone, and it comes in a beautiful blue-violet shade. These beauties are easier to source and they provide a beautiful color.

However they’re fairly soft, scoring a 6-6.5 on the Mohs scale so always use a bezel setting and be very careful when wearing them. You may not want to wear this stone on an everyday basis.

Lapis lazuli

Lapis lazuli is a very old, ancient stone and it’s very different from sapphire. First it’s not a clear stone, not even translucent. It’s an opaque stone but it has the most beautiful deep blue color with golden streaks. On a cut and polished piece the gold may look a bit like scattered glitter, or it may look like a gold vein, depending on each stone in particular.

You’ll find lapis lazuli commonly cut into cabochons, and they’re nearly always in a bezel setting. These soft stones score a 5-6 on the Mohs scale, so be careful with them.

Blue cubic zirconia

If all else fails and you really, really can’t find anything else you like, why not try a blue cubic zirconia ? These are lab grown diamond dupes, so they will be available in any color you want, including sapphire blue.