Corundum Conundrum – Ruby vs Pink Sapphire

There’s an old adage in the jewelry industry: “If you’re the seller, it’s a ruby; if you’re the buyer, it’s a pink sapphire.” The world of colored gemstones is by no means as highly organized or regulated as is the world of diamonds.

By comparison, diamonds are fairly simple and straightforward. Colored gemstones comprise the other 99.99% of the gem world. Like diamonds, some colored gems can command tens or even hundreds of thousands of dollars. Some colored gems will even surpass most diamonds in price. Chief amongst these are rubies.

For thousands of years, all red gemstones were carbuncles, a word which means “a smoldering coal.” Gem miners and fashioners of Antiquity noted obvious physical differences in working various materials of the same color, but for the most part, little distinction was made to consumers. As modern gemological science progressed, divisions started being made between species on a chemical level, separating ruby from other naturally red gems like spinel, garnet, tourmaline, and zircon. But after species lines were delineated, at the end of the day, this only rehashed the original question of color within species. Now it’s a matter of color nuance.

Enter corundum. Not familiar with that? Corundum is the mineralogical name for sapphires and rubies.

The difference between a ruby and a sapphire is color. Chemically speaking, they are both aluminum oxide – corundum. Pure corundum is colorless. Sprinkle some iron and titanium into the mix and you’ve got a blue sapphire. If iron is the only coloring agent, yellow will be the color base.  A little nickel goes a long way to making green sapphires. Start adding chromium to the basic corundum formula, however, and you’ll get into murky territory.

Technically speaking, pink is just a paler shade of the color hue red; it is the strength of the red that makes a ruby a ruby. But there is a point where the line becomes blurred. Depending on the size and clarity of a given stone, the price difference between a ruby and a pink sapphire can be anywhere from a few hundred dollars to tens of thousands of dollars, hence the conflict. In the image below, where is the line between ruby and pink sapphire?

Suite of red corundums

Usually, the matter is settled by sending the stone to the Gemological Institute of America, or some other respected gem lab, for grading. In my store, I prefer to solve the problem proactively by trying not to stock or sell desaturated red corundum that blurs the line. That way, there is never any confusion between the pink sapphires and rubies that I carry.