Spinel is a mineral that owes its beautiful color to chromium, much like rubies and emeralds do.

1. It has a hardness of 8 on the Mohs hardness scale (diamond has a hardness of 10).
2. Spinel is seen in a wide range of colors: red, lavender, violet, blue, green, brown, black.
3. Often, spinel is found in gravel deposits where there is much corundum as well.
4. Spinel typically contains magnesium and aluminum.
5. The chemical formula for spinel is MgAl₂O₄.
6. Spinel is singly refractive, often transparent, with a specific gravity of 3.60 and a refractive index of 1.718.
7. Spinel crystals have no true cleavage.

What is the value of a spinel gem?

Now that we know the science basics of spinel, what makes it such an interesting gemstone?

Well, it wasn’t always easy to tell the difference between a deep red spinel and a ruby. They were often found in the same places, and once polished, the two gems were nearly indistinguishable. And without the scientific equipment we have today, it was much more difficult to differentiate the two gemstones—it wasn’t until 1783 that a mineralogist discovered they were not, in fact, the same thing.

That’s why many historical crown jewels actually contain spinels, and not rubies. In fact, some spinels are called “balas rubies,” named for this similarity and the Balascia region in which they were often found.

One of the most famous spinels in the world is the Black Prince’s Ruby, the 170-carat gem that adorns the U.K.’s Imperial Crown. And the Timur Ruby, also part of the British crown jewels, is actually a 361-carat polished red spinel. The Black Prince’s Ruby is the largest uncut spinel in the world, and once decorated King Henry V’s helmet during battle.

You may be surprised to know that spinel is rarer than ruby, but this has not affected its price (yet). Although spinel is still less expensive than ruby, the market for spinel has been increasing.

And, now that spinel has been added as a third August birthstone, its popularity may increase further still, bringing its value up as well.

While it can be difficult to say exactly how much a spinel gemstone costs, because price depends on so many factors, there have been some eye-popping price tags.

Where does spinel come from?

So, where to find this incredible gem? Spinel can be found on several continents, from Brazil in South America, Kenya in Africa, and especially across the southern portion of Asia, stretching from Afghanistan to Vietnam. It has been commonly found in gravel beds in Sri Lanka, Tanzania, and Madagascar, and marble deposits in Vietnam.