Spinel is a magnesium aluminum oxide gemstone found naturally in deposits across Asia, the Middle East, and Africa. It is not well-known outside the gem and mineral industry, although it has famously stood in for rubies, and in some cases has been involved in cases of mistaken identity. The Black Prince’s Ruby in the British crown jewels, for example, is not actually a ruby, but a spinel. This mineral can be produced synthetically in lab environments.
These gems are examples of metamorphic stones that form when intense heat and pressure transform existing rock deposits. They tend to form cubic crystals and are prone to a twinning formation. Some are clear, but they also come in an array of colors red, pink, blue, and green. Some of the most notable examples have been pink to red.
On the hardness scale used to assess minerals, spinel measures an eight. This is one of the highest rankings on the Mohs scale, close to that used for rocks like diamond. The strength makes it an extremely durable stone, capable of enduring harsher conditions than more fragile gems. It is also relatively rare in nature, with some of the best deposits located in Myanmar.
Historically, some spinels were passed off as rubies, sometimes accidentally. Although recognized as its own distinct mineral, the spinel sometimes stands in for rubies for security reasons. With very large and precious stones, it is not uncommon to take a gem out of the setting and replace it with a less valuable ringer for public displays. This allows people to showcase their jewelry without running the risk of losing an extremely large and valuable stone.
Both synthetic and natural spinel can be used in jewelry. Synthetic versions are chemically identical to natural stones, and have similar structural characteristics. The stones can be washed with warm water and mild soap if they get dirty, and it is also safe to run them through ultrasonic cleaning machines and similar devices. While spinel is sometimes treated as a poor imitation of ruby, individual stones can be quite valuable and may fetch high prices at market if they are pure and have a strong, good color.
Jewelry stores may carry spinel pieces and can order or fabricate them by request from customers. Like other stones, it can be assessed for signs of inclusions and other impurities that might degrade the quality. The color can also be graded in terms of intensity and hue.