Sapphire’s high hardness means it’s very resistant to scratching. Thus, it makes an excellent jewelry stone for any occasion. These gems also show pleochroism, two different colors when viewed from different angles. In rare cases, mineral crystal inclusions can create star sapphires, specimens that display a “star stone” effect known as asterism. Some rare gems can also change color, depending on the light source. 

However, since gem-quality natural sapphires are rare and the demand so great, you’ll commonly find synthetics and imitations on the market. They also frequently receive treatments and enhancements for the same reasons.

What is a Sapphire?

Gem-quality corundum falls into two categories: ruby or sapphire. All red corundum gems (however defined) are considered rubies. All other colors are considered sapphires. Thus, sapphires occur in every color except red.

Commercially, blue sapphires are commonly referred to as simply sapphires. This reflects not only the persistent cultural association of sapphire with the color blue but also the consumer demand for blue sapphires. You may find sapphires of other colors referred to as “fancy sapphires.” Nevertheless, all sapphires are non-red corundum gemstones. When discussing optical and physical properties, “sapphire” refers to all sapphires regardless of color.…