September Sapphires and July Rubies, Or How I Hit Two Gems With One Stone

Sapphires can be any color ““ blue, green, purple, clear, yellow, maybe even a little orange or pink ““ but they can’t be red. Even orange is a little questionable. Pink is sort of on the fence. OK, now I’m just stalling before the big reveal: sapphires cannot be red because if they are red they’re called rubies.

A photo of the Logan Sapphire, which at 422.99 carats is the second largest blue sapphire. Now that is a rock. Uploaded to wikicommons by user Deerstop.

Before I get into the science of these gemstones, can I just say that I think it’s a little bit of a racket that out of the four truly precious gemstones (diamonds, emeralds, sapphires, and rubies), two of them are actually the same thing, just with slightly different colors? I guess I could see this as a great deal (two for one!), but mostly I’m just bummed that rubies and sapphires are basically the same thing after thinking they were different, cool, unique rocks for so long. OK, disappointed rant over ““ now, back to the science.

Sapphires and rubies are the precious gem versions of the mineral corundum, which is in turn the hard, crystalline version of aluminum oxide, a common material with many industrial uses. Aluminum oxide forms when aluminum is exposed to air. A patina of this aluminum oxide covers all aluminum, and since it is a fairly inert material, it doesn’t react much when it comes in contact with other chemicals.

When  you take this inertness and combine it with a Mohs hardness rating of 9 (only moissanite at 9.5 and diamonds with their 10 can top it), you got yourself a strong, durable stone that’s used in a wide variety of fields and applications, really anything from an abrasive to rival industrial diamonds to insulation in high temperature furnaces. And of course the gems get used to give humans a bit more sparkle.

This is a ruby gemstone with some inclusions, meaning some sort of material that got trapped in the gem while it was being formed. Photo uploaded to wikicommons and created by user Humanfeather.

Natural sapphires and rubies are formed over millions of years and are brought to the earth’s surface by volcanic activity. These gems can be found in both igneous and metamorphic rocks. They’re the home-bodies of rocks: once they get weathered out of their source, they don’t usually travel too far. Because sapphires and rubies are the same basic thing, they are often found together ““ they are gemstone BFFs.

One of the most important factors in deciding the value of a sapphire or ruby comes from the color, and here is where we see the one difference between sapphires and rubies: rubies get their distinctive red color from the presence of the element chromium and only chromium, while the wide range of sapphire colors comes from presence of iron (yellow and green) and/or titanium (blue), and some combination of iron and/or titanium with chromium (pink). When dealing with blue sapphires, a purplish undertone is considered more valuable than a green one, but to each their own and personally, I think green is gorgeous (please read that word as if I am stretching it out like a fabulous old lady talk about a brand new bag or something).

I would wear this sapphire necklace so hard. Photo of necklace at the National Museum of Natural History in Washington D.C. Photo by dbking, found on wikicommons.

Since most of the value lies in the color, many sapphires and rubies are color-treated to enhance the color and thus increase the value of the stones, just like the topaz I talked about a few weeks back. Both stones can be heated to improve the color, and sapphires are sometimes irradiated. And if just futzing around with color isn’t enough for you, whole sapphires and rubies can be created in a laboratory (diamondnexuslabs explains one of the processes clearly in one concise paragraph, which is better than what I could do, so I am just linking them here).

Given that controlled setting, the color and clarity of the lab-created stone can be absolutely top notch. While lab-created stones sell for less than natural ones, they are advertised as a good alternative to natural stones if you’re concerned about humans right issues associated with mining, and the impact of mining on the environment (though to be fair, I haven’t really found any analysis of the environmental impact of lab-created stones). This is not to say that there aren’t any ethically mined sapphires and rubies (there are), it’s just a head’s up.

3 replies on “September Sapphires and July Rubies, Or How I Hit Two Gems With One Stone”


Nice write-up on the sapphire, it really is one of the best gemstones out there.

Given that controlled setting, the color and clarity of the lab-created stone can be absolutely top notch.

In fact, one of the easier ways synthetic sapphires are distinguished from natural sapphires is that a synthetic one will be internally flawless. While every natural sapphire will have atleast some inclusions, though perhaps only visible through a microscope.


Insaint (

Yay Sapphires! As someone with a September birthday, I’ve always been a fan of sapphires. And I didn’t know they were the same, technically, as rubies! But enough with my joy at shiny things –

While you touched on the human rights issues with mining, I wanted to point out that sapphires and rubies from Burma have a lot of the same issues that “blood diamonds” do from Africa – they’re being used to fund a horrific, long-standing conflict that isn’t getting nearly enough international attention. As the concept of blood diamonds has gotten more popular, I know a lot of people are turning to sapphires, rubies and emeralds as a conflict-free alternative, but, depending on where they’re coming from, these gemstones can have just as high of a death toll. So please, if you’re buying jewelry, see if you can find out where the stones come from! I don’t think there’s an equivalent of the Kimberly process for sapphires, but still, a bit of research goes a long way.

Leave a Reply