What’s Your Birthstone?

Garnet brooch, gemstone

Before the holidays, inspired by my gemology class, I posted about diamonds and pearls (for any last-minute shoppers among my readers), but of course, there’s much more to gemstones.

The majority of gems in the jewelry industry (including at least 95 percent of the diamonds) are “enhanced” to some degree, the class leader—an expert gemologist—explained. Enhancements and treatments can change or remove color; improve clarity, luster, or durability; fill fractures; or, in the case of star rubies or star sapphires, accentuate their stars (“asterism”). Sellers are “required” to disclose such treatments, especially if the stone needs special handling as a result, and the most reputable jewelers do. We crime writers are more interested in the disreputable ones.

Treatments typically include heating the stone (with sometimes unpredictable results), filling fractures (emeralds, especially), bleaching (pearls), irradiation, and exposing the stones to a chemical vapor. Sometimes these enhancements are merely superficial and the results may not last. Another opportunity for shady dealing!


Many of us have a fondness for our birthstones. My January birthstone is garnet, a semiprecious stone (a nesosilicate) that comes in a lot of colors besides the deep red the Victorians loved (as in the brooch above). The green version, for example, is called tsavorite. Different families of garnet are of different chemical compositions, including trace amounts of other elements that affect the color. Tsavorite has a bit of vanadium or chromium.

If you were born in February, your birthstone is amethyst, a type of quartz. The best ones are a deep, rich purple and the ancient Greeks believed amethysts protected their wearers from intoxication. That would be a property well worth fictional exploitation. If an amethyst is heated, it turns yellow, in which case it’s called citrine.

gemstone, aquamarine

The March birthstone in centuries past was bloodstone, an opaque dark green stone with red flecks. Its replacement, aquamarine (pictured), is a type of beryl, as is the May birthstone, emerald. Emeralds are much rarer (and therefore, more valuable), but full of inclusions (flaws) that make them brittle. A candid jeweler may recommend an emerald as “a Sunday stone,” too prone to breakage for a ring you plan to wear every day.

You might think diamonds would be the June birthstone—all those brides–but no, they’re the stone for April, and June’s birthstone is pearls. Both covered in a previous post.

gemstone, sapphire

July (ruby), pinker than garnet, and September (sapphire, pictured) are closely related. They’re both forms of the mineral corundum (aluminum oxide). The red color comes from chromium; traces of a variety of other minerals produce “sapphires” that can be yellow, green, or other colors, or the iconic deep blue. Only the red version is called a ruby.

The August birthstone also has changed over the years. To my mother, born August 1, her birthstone was carnelian (sardonyx), a type of chalcedony, and she wore a beautiful carved carnelian ring. But at some point, the marketing wizards decided more birthstones should be “fancier” transparent gems, and the August stone was changed to the pale, yellow-green peridot. It’s one of the few gemstones that comes in only one color.

October’s birthstone is opal, which is becoming increasingly rare and, therefore valuable. “Precious opal” displays “play-of-color” across its surface, caused by minute spheres and voids within the stone that break up white light and reflect back colors. Wrap one in a bay leaf, and become invisible, people in the Middle Ages believed, something an opal thief would be happy to know about, if it works. Our instructor said she’s often asked, “Should I buy an opal?” and her answer is, “Yes! Twenty years ago.”

The birthstone for November is topaz—another stone that comes in a variety of colors, depending on trace minerals. It can be yellow, golden brown, pale gray (smoky topaz) or a variety of other colors. Mentions of topaz can be found in the Bible, and in ancient times,  it was considered a protective stone. Blue topaz is sometimes passed off as a more valuable stone.

turquoise, silver, jewelry, earrings

Finally, the December birthstone, bucking the penchant for transparent stones, is turquoise in the vintage earrings shown. If you admire the turquoise jewelry from the American Southwest, you know there is a range of shades from green to blue, and you may also know about the booming market in fake turquoise. Turquoise is a form of copper and aluminum and gained its name from the French word for “Turkish,” Turkey being the initial source of the mineral for Europeans.

Whenever your birthday falls in 2021, I hope it’s a good one. Celebrate by decorating yourself with your own special birthstone!

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