Step 1: Introduction to Gemology

Lesson 2

For thousands of years, people have used terms like “gem” and “gemstone” to describe objects like rubies and emeralds. However, some find defining a gem quite challenging. Not everyday people with common sense but people like lexicographers, who need to define each word in our language very precisely. I feel sorry for them, simply because no concise definition covers all the materials that have been regarded as gemstones throughout the centuries.
inlaid pendant

A 14k yellow gold pendant featuring inlaid sections of lapis lazuli, jet, spiny oyster, and opal. Photo courtesy of liveauctioneers.com and Hindman.

A Working Definition of a Gem?

The following definition covers the vast majority of the stones we regard as gems:

Minerals that have been chosen for their beauty and durability, then cut and polished for use as human adornment.

Still, every defining feature in that definition has exceptions. This creates problems.

Are All Gems Minerals?

Most gems are minerals, but some — notably pearl and amber —  are organics. Living organisms create these materials. By definition, a mineral must be created inside the Earth. Hence, pearls fall into a different category. (To add some confusion, a pearl’s coating is a mineral, even though pearls form inside a mollusk). Likewise, amber began life as tree sap. After millions of years, it transformed into a polymer, a natural plastic. People have regarded amber as a gem for thousands of years, although it’s definitely not a mineral.

what is a gem - amber

Although frequently called fossilized tree sap, amber isn’t a fossil. Fossilization occurs when minerals replace organic matter buried in the Earth over the course of millennia. Amber’s organic elements have not been replaced by minerals. Sometimes, amber pieces contain inclusions of ancient insects and other creatures trapped in the tree sap. These can often add interest and value to amber jewelry. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Must a Gem Be Beautiful?

Some people would consider gems colored Pepto-Bismol pink and olive green unattractive — like unakite, a variety of epidote. Some find them beautiful. Brown gems enjoy some popularity in “earth tone” jewelry pieces. Of course, others have different tastes. Beauty may be in the eye of the beholder, but do all who choose gems choose beauty? Do all gem enthusiasts select gemstones because they find them beautiful?

gem definitions - unakite

With a green fabric braid and Japanese seed beads, this brooch features a unakite center stone. Jewelry and photo by Medusa Jewellery. Licensed under CC By-ND 2.0.

How Durable Must Gemstones Be?

For gemstone buyers, durability is usually a high priority. Nevertheless, two very popular gems are particularly delicate. Pearls generally last about a century as jewelry stones due to their softness. The simple act of wiping off dust will slowly wear away their coating. Perfumes and hairsprays can also stain and damage pearls. As ring stones, pearls need protective settings, especially for engagement rings.

pearl bracelet

Pearl bracelet. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Highly valued throughout history, opals are notoriously delicate. As they lose their high water content, they dry out and may crack. They may break with the slightest bump. They’re heat sensitive, too. I knew one customer who had a prized opal brooch in a protective setting. One night, as she left a Christmas party, the opal shattered with an audible crack as she went from the warmth indoors to the cold winter night. Many have shed tears over opals, and that has even contributed to the belief that opals bring bad luck.

opal

Opal. Photo by jimthompson. Licensed under CC By-SA 2.0.

Must All Gems Be Cut and Polished?

So much for beauty and durability. How about cutting and polishing? Currently, many people love using whole crystals or “raw stones” in jewelry. In decades past, this wasn’t the case. Mother Nature’s crystals can be exceptionally beautiful. Some even believe they have special metaphysical properties that are enhanced when left whole. So, we can’t insist that our gems be cut and polished, either.

red beryls

Found only in the Wah Wah Mountains of Utah, red beryls are some of the rarest and most coveted gemstones. However, crystals are always small, like the ones in this photo, and make prized mineral specimens. Faceters very rarely have a chance to cut them. © Rob Lavinsky, www.iRocks.com. Used with permission.

Can All Gemstones Be Worn as Jewelry?

The last qualification usually associated with a gemstone is its use for adornment. People have cut, polished, and admired about 3,000 minerals. Of these, only about a hundred show up in jewelry. The rest are simply too delicate to wear well and fall strictly in the collector’s domain.

gem definitions - cinnabar

The mine that yielded this beautiful cinnabar crystal on a quartz matrix has been in operation for over 2,000 years. Since ancient times, people have used cinnabar for carvings and to manufacture red pigment. This material is not only too soft for jewelry use but also toxic. It’s used principally as mercury ore. Cutting this gemstone would require great care. Almaden, Almaden District, Ciudad Real, Castile-La Mancha, Spain. © Rob Lavinsky, www.iRocks.com. Used with permission.

A Not Quite Scientific Definition of a Gem

Gemology was first recognized as a science only in the 1930s. Until that time, many people considered all transparent, red gems rubies, blue ones sapphires, and green ones emeralds. Today, as a professional gemologist, I can only call a crystallized beryllium-aluminum silicate with trace amounts of chromium or vanadium an emerald. Other beautiful green gems could be tsavoritestourmalines, diopsides, and even sapphires.

The allure of gemstones lies in their fantasy of color and light. Beautifully colored stones have intrigued people since time immemorial. The love of gems hasn’t changed. However, we now have to contend with a very scientific element. As much as I love the science of gemology, it has the unfortunate side effect of taking much of the mystique and romance out of our stones.

To heck with the definitions. If it makes your eyes light up, it’s a true gem!

gem definition - green sapphire

Green isn’t just the domain of emeralds. Although best known for the color blue, sapphires occur in many colors, including green, like this rectangular step-cut specimen from Sri Lanka. 1.18 cts, 6.5 x 4.8 mm. © The Gem Trader. Used with permission.