How Well Do You Know Your Birthstone Gemology?


You might be familiar with the romance of birthstones, but how well do you know birthstone gemology? Take our short quiz and learn about the composition, faceting, and value of birthstones.

birthstone ring
A diamond and sapphire ring.

What Is My Birthstone?

Throughout history and across cultures, people have given poetic meanings to different gemstones. Today, our use of birthstones is probably the best-known example of this practice. A special stone is assigned to those born in a particular month and is said to be their “good luck” stone. The gems and their meanings vary across cultures. Below you’ll find a list of birthstones commonly used in English speaking countries.

MONTH

MODERN

ANCIENT

January Garnet Garnet
February Amethyst Amethyst
March Aquamarine Bloodstone
April Diamond Diamond
May Emerald Emerald
June Alexandrite Pearl
July Ruby Ruby
August Peridot Sardonyx
September Sapphire Sapphire
October Rose Zircon Tourmaline or Opal
November Golden Topaz Topaz
December Blue Zircon or Tanzanite Turquoise or Lapis

The “modern” list was created in the early 20th century. However, it hasn’t really replaced but only supplemented the “ancient” list. Nowadays, people freely choose between modern and ancient options. (There are also many alternative birthstone lists in use, including astrological birthstone lists and birthstones based on the hour of birth).

Birthstone Gemology Questions

  1. Which birthstones are minerals?
  2. Which birthstones are usually cut as cabochons?
  3. Which birthstones are the most valuable?
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“Sterling Silver Ring with Bloodstone Inlay” by Jessa and Mark Anderson is licensed under CC By 2.0

Birthstone Gemology Answers

1. All the birthstones are minerals, except pearls.

Minerals are created in the earth. Pearls are considered “organic” because they are created in a living organism, an oyster. Another example of an organic gem is amber. Amber began life as tree sap. After millions of years it became fossilized into the gem we know today.

Pearl Extraction
Pearl extraction.

2. Bloodstone, sardonyx, opal, turquoise, and lapis are usually cut as cabochons.

Although all birthstones (except pearls, which are never cut) could be cut as cabochons, the transparent gems (garnet, amethyst, diamond, emerald, ruby, sapphire, tourmaline, and topaz) are more commonly cut as faceted gems.

Cutting en cabochon, or as it is more commonly known, “cutting cabs,” is the most common form of gem cutting. Cabs are gems that are cut with a flat bottom and a curved or domed top. This method is commonly used for opaque stones or transparent ones with a lot of inclusions.

Opal Cabochon Brooch
Cabochon cut opal brooch.

If you can envision a diamond, you are probably imagining a faceted gem. Faceting is a style of cutting used on transparent stones. The surface of a diamond, for example, is covered with several geometrically arranged, flat surfaces. Each of these flat surfaces is called a facet. The gem is faceted on a faceting machine.

The purpose of faceting is to bring out the brilliance of a gem. That is where the light entering the stone is reflected from inside the gem, back to the viewer. Brilliance should not be confused with fire, the multicolored flashes you see coming out of diamonds and some other gems.

3. Diamond, emerald, ruby and sapphire are typically the most valuable birthstones. However, there is no simple answer to the question of value.

The value of a gem depends on four qualities, which are frequently known as the Four C’s.

  • Color. Gems are not created equal and the richer the color, the higher the value. With diamonds, the closer they are to being colorless, the higher they are in value.
  • Clarity. If a gem is completely transparent, it will be worth more than one that is hazy. All gems have inclusions, which means things inside them. These can be cracks or bits of other minerals. Some are so small they can’t be seen and have little or no effect on the value. Others are big and ugly!
  • Carat. This is the gem’s size. Big gems are more rare than little ones.
  • Cut. How well a gem is cut or faceted has a lot to do with its beauty.

Diamonds may be popularly considered to be the most rare and most expensive gems, but that is not truly the case. Rubies that weigh over a carat are more rare than diamonds of that size. A three-carat ruby, with excellent color and clarity, can be worth more than a diamond of the same size and clarity.

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“Five-Carat Ruby Engagement/Wedding Ring” by 3BL Media is licensed under CC By 2.0

Emerald grows fairly large, so size isn’t as important a consideration as with ruby. However, emeralds almost always have visible inclusions. A top colored diamond, with the same amount of inclusions as a top colored emerald, would have less value.

How well a gem is cut or faceted greatly affects its beauty and value. Just imagine a diamond that sparkles with fire and light! Next to it is a diamond that looks dull, like a piece of cut glass. That is the difference faceting can make.

 

About the author
Donald Clark, CSM IMG
Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters "CSM" after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff's ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book "Modern Faceting, the Easy Way."
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