Spinel

Spinel is most famous for its deep red variety that closely resembles Ruby. These two gemstones can be very difficult to distinguish. Until the late 19th century, there was no distinction made between Ruby and red Spinel, as they look identical and are found in the same localities. Many famous old "Rubies" were discovered to be in fact Spinel. For example, the enormous "Ruby" that forms the centerpiece of the royal crown of England (the Black Prince's Ruby) was actually determined to be Spinel.

Spinel is a gemstone that comes in a variety of colors. Pure Spinel is colorless, but impurities are responsible for the wide range of colors. The most valuable and desirable Spinel color is a deep blood red, though blue, yellow, orange, pink, and purple colors also make fine gemstones. Spinel is often fluorescent in ultraviolet light, and this can be helpful in its identification.

Fine red Spinel is actually rarer than Ruby of equal color. However, its  is an undervalued gemstone, with its cost is about 30% lower then comparable Ruby. The scarcity of good Spinel is the reason for its lack of demand and popularity. Gem Spinel is in very limited supply, and therefore jewelry companies and gem cartels don't really market this gemstone to the consumer. This inhibits Spinel from being a more mainstream gemstone.

Spinel is easily synthesized, and can be made into any color by adding impurities. Synthetic Spinel is often simulated to replicate many other gemstones such as Diamond, Sapphire, and Zircon. Because of the abundance of synthetic Spinel, one must always be careful only to purchase this gemstone from reputable dealers. Almost all colorless Spinel gemstones are synthetic, as it rarely occurs colorless in nature.

Sources:

The most outstanding Spinel in size, color, and quality is from Burma. Other sources of gem Spinel are Sri Lanka, Cambodia, Vietnam, Thailand, Tadjikistan, Afghanistan, Pakistan, Tanzania, and Madagascar.

Similar Gemstones:

Red Spinel can be identical in appearance to Ruby. However, Spinel is usually lighter in color, and the deep-red Spinel is usually more of a brick-red then the Red of Ruby which has a slight blue or purple tinge to it. However, only optical properties and hardness can truly distinguish these two gemstones. Red Spinel can also closely resemble red Tourmaline and dark red Spinel may resemble Garnet.

Blue Spinel may resemble Zircon, Topaz, and Sapphire; and pink Spinel may resemble Morganite, pink Topaz, and pink Tourmaline. Purple Spinel may appear similar to Amethyst, though Spinel is usually bluer in tone than Amethyst.