Gemstones and Birthstones: Ruby — Just the Facts

It’s mid-summer and most of us are feeling the heat (in the Northern Hemisphere, anyway), so it seems appropriate to celebrate the July birthstone which has the hottest color of them all: brilliant red ruby.

ABOVE: Rubies make a spectacular color spot in Andy Cooperman’s Hunter’s Horn Brooch. Sterling, 14k rose gold, 18k yellow gold, square-cut ruby. Courtesy Andy Cooperman.

Rubies are actually red sapphires. Sapphire (and ruby) are the names given to colored varieties of corundum. (Aluminum oxide, if you want to get personal.) Their gorgeous colors, of course, have made rubies and sapphires highly sought after for millennia. But that’s not the only reason why they’ve achieved “rock star” (ouch!) status. If any gemstone is virtually indestructible, it’s this one.

Gemstones and Birthstones - Rubies and all their glorious red juiciness!

2.72 cts cushion-cut Burmese ruby. Photo by Mia Dixon. Courtesy

Rubies are extraordinarily hard. (Next to diamond’s 10, rubies are a 9.) And they’re tough. Diamonds have cleavage directions that can cause them to split if they’re hit hard and hit just right. But corundum, including ruby, does not have those directions of weakness. A ruby will wear (or abrade) if it’s rubbed against other rubies, sapphires, or diamonds, but it will take a lot to break one. Many years ago I saw an early 20th Century wedding ring set with three large, rich blue sapphires. The once-faceted stones had been worn, over decades of marriage, almost into cabochons. But they had never chipped. Rubies would have endured as well.

Facet design by Jim Perkins: Lilly’s Trillion, cut in synthetic ruby by the designer’s granddaughter; photo: Jim Lawson

Facet design by Jim Perkins: Lilly’s Trillion, cut in synthetic ruby by the designer’s granddaughter; photo: Jim Lawson. From the May/June 2019 issue of Lapidary Journal Jewelry Artist.

Rubies are also one of the most heat-resistant stones you’ll meet at the bench. In days past, if a ruby was free of fractures and large inclusions [please note these very significant caveats!], jewelers might use a torch to repair a piece of jewelry with the rubies in place. Of course, if they missed spotting a crystal inclusion, it could expand and shatter the stone. Something that’s tough to explain to a customer.

Please note that soldering with a ruby in place is not advised! It’s not unusual for rubies today to be glass-filled to hide imperfections. Heat a glass-filled ruby, and you’ll have a really big—and potentially very costly–mess on your hands!

Rubies are truly gemstones for the ages. Whether you’re wearing a naturally colored or heat-treated stone, or a ruby created in a laboratory, the ruby’s gifts of color and endurance are ones you will enjoy all your life.

Sharon Elaine Thompson is a GG and FGA who has been writing on gemstone and jewelry topics for Lapidary Journal Jewelry Artist since 1987. She also writes a line of Birthstone Romances under the name Liz Hartley.

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