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All About Sapphires

Posted by Danny Mosco on

This month we are going to talk a little bit about sapphires. Oh, where do even begin? There are lots of different things to talk about when it comes to sapphire, but we will give you a broad overview of various aspects of the stone, such as: the different kinds of sapphires you can get, how sapphire is formed, the types of treatment for the stone, where sapphire can be found in the world, and the criteria to determine a sapphire’s quality.

Blue sapphire is a mineral species known as corundum, as can range in color from a pure deep blue, to a greenish blue, to a purplish blue. People use the name “sapphire” to refer to any corundum species which isn’t red. Red corundum is actually ruby, which interestingly means that rubies and sapphires, but for their color, are basically the same thing. The corundum family also applies to what are called “fancy sapphires,” meaning the ones that come in violet, green, yellow, orange, pink, and various other hues. Some sapphires even have combinations of different colors in them, which is really unique! Other sapphire stones exhibit the effect known as color change, where the stone is blue in regular daylight and fluorescent lighting, and looks more purple under incandescent light. Fancy sapphire colors are generally more scarce than the blue ones are, especially when it comes to the larger sized stones. Fancy sapphires come in every color except red, which is known as ruby.

Corundum is actually only made of aluminum and oxygen, and needs an environment free of silicon, but it’s very rare for that to be the case. Natural corundum has no color at all, which actually made colorless sapphires popular as a diamond substitute. Depending on what trace elements are present is what causes the sapphire to get its color. For example, trace elements of iron and titanium causes the corundum to become blue. Corundum can also display a phenomenon known as asterism, or more commonly known as the star effect. It looks like a star pattern with 6 rays appearing across a cabochon cut stone’s surface. It actually comes from white light reflecting from countless tiny, needle-like inclusions in the stone. This is what we call “star sapphire.”

There are a couple of kinds of treatment most commonly used for sapphires: heat treatment and lattice diffusion. Heat treatment is simply exposing a gem to high temperatures for the purpose of changing its color and/or clarity. In sapphires, heating can really enhance, or even to a certain extent cause, a blue coloration. Heating can also take away “silk” type inclusions, which makes the sapphire appear to be more clear and transparent. Conversely, the heat treatment can also cause recrystallization of the silk inclusions to make them more apparent, which is desirable for the purpose of making the stone have stronger asterism (the star effect). Lattice diffusion is defined as, “The penetration of certain elements into the atomic lattice of a gemstone during heat treatment, with the objective of changing or accentuating its color” (GIA.edu). This diffusion is related to the heat treatment process, but it takes it one step further. During heat treatment, substances are in injected into the stone for the purpose of making the color even stronger. This process was first being experimented with in the 1980s, but was met with little success. Titanium and chromium (coloring agents in corundum) were being used to try to get the color of the stones richer, but it wasn’t until 2003 when a more effective method was discovered. Beryllium was used, which proved to be far more effective because of its ability to penetrate all the way through a sapphire, even the larger ones. Beryllium also worked well on rubies.

Sapphires come from many different areas of the world, ranging from Madagascar, to Tanzania, to Thailand, to Australia, to China, to Cambodia, and Montana. Montana is the only place in North America that has sapphires. Each region of the world produces unique colors of sapphire.

Determining the quality of sapphire is dependent on a number of factors, and we will try to be brief as we summarize them. There 4 main criteria: color, clarity, cut, and carat weight.

Color – Color is the most important element in determining the value of a sapphire. The most valued blue sapphires have a velvety blue color to a violetish blue. Choice sapphires have strong color saturation as well, where the saturation should be as strong as possible without compromising the color by making it too dark, and losing brightness.

Clarity – Clarity is all about how many inclusions are in the stone. Blue sapphires usually have some inclusions, but are typically clearer than rubies are. There are different types of inclusions found in sapphires, but one of the most common ones is what are called “needles.” Finer needles are called silk (as you recall, this is actually where the star effect comes from). Some other clarity factors are included mineral crystals, partially sealed breaks that look like fingerprints, color zoning, and color banding. More inclusions = a less valuable stone.

Cut – The cut of the sapphire is simply the shape of it. Gem cutters cut the stones to focus on preserving the best proportions, and maintaining weight. Most stones should be cut to have the dome of it pretty high, approximately two-thirds of the stone’s width. This is especially important for star sapphire.

Carat Weight – This makes the most difference when comparing the carat weight of fine sapphires to large commercial quality blue sapphires. A 5 carat fine-quality sapphire will typically run about 5 times more expensive than a 1 carat fine-quality sapphire, whereas a commercial quality will usually only be about 2 times more expensive.

And there you have it – some broad overview guides to sapphire! We love this stone and very glad that we carry it as part of our product line.

To read more in depth, check out these sources we used:

https://www.gia.edu/sapphire#gem-overview

https://www.gia.edu/sapphire-description

https://www.gia.edu/gem-treatment

  • sapphires
  • sapphire
  • birthstone

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