Understanding Gemstone Inclusions and Other Gem Info for Jewelry Makers

Being a gem geek extraordinaire, I was thrilled when I learned we had a new book coming out about gemstones. Judith Crowe’s Gemstones: A Jewelry Maker’s Guide to Identifying and Using Beautiful Rocks is a maker-friendly guide designed to help jewelers and jewelry makers in “identifying, buying, using, and caring for a dazzling array of jewels and gems.”

ABOVE, clockwise from left: Tourmaline faceted beads showing the wide range of colors that the gemstone can be found in. Tourmaline is colorless in its pure form, but trace elements and chemicals will give the gem a variety of colors, making it an allochromatic gem. Golden yellow topaz faceted pears: Some gemstones have planes of weak atomic bonding (cleavage). Topaz has cleavage such as this, so if it is used in a ring it requires a protective setting. These peridot cabochons will always be green because they are idiochromatic gems. Iron impurities are not only the coloring agent of the gem but also an important part of peridot’s chemical composition. Chalcedony (carnelian): This specimen shows chalcedony’s botryoidal microcrystalline habit, which is a compact mass of tiny trigonal Quartz crystals. Aventurescence is an optical property that can appear in aventurine quartz, sunstone (shown here), labradorite, and obsidian. 

Gemstone Inclusions: Friend or Foe?

I could write for days about all of the things I love about gemstones. But a gemmy topic that we rarely talk about is inclusions. Are they good or bad? Gemstone inclusions can go either way. They can add to or reduce a gem’s value and beauty (though the latter is subjective). They’re also helpful in gem identification, in determining whether a stone is natural or synthetic, if it is treated, and its source.

Dendritic agate A great example of dendritic agate showing the black dendrite crystal formations in the milky agate, which look like trapped plant-life but are small crystals. It is completely natural--no treatments have been used.

Dendritic agate
A great example of dendritic agate showing the black dendrite crystal formations in the milky agate, which look like trapped plant-life but are small crystals. It is completely natural–no treatments have been used.

I’m a fan of gemstone inclusions. Like freckles on humans, inclusions are so very one of a kind. They appear in various patterns and types, making each gem even more unique. So let’s learn more about gemstone inclusions in this excerpt from Crowe’s book.

Amber cabochon with insect inclusion Amber was the sticky resin of pine trees, so inclusions of plants and insects can frequently be found. This cabochon has a fully intact fly-insect inclusion, which gives it added interest and value

Amber cabochon with insect inclusion
Amber was the sticky resin of pine trees, so inclusions of plants and insects can frequently be found. This cabochon has a fully intact fly-insect inclusion, which gives it added interest and value

Understanding Gemstone Inclusions

From Gemstones by Judith Crowe

Inclusions are the internal structures and features found inside a crystal or gemstone; they can be solids (such as small crystals of another mineral), liquids (such as silica droplets), or gases, or they can be semi-filled fractures or cleavage breaks. They occur during the formation of the crystal, which can envelope the inclusion as it forms or, in the case of fractures, occur at the same time as the host material is forming. Some inclusions are unique to particular gemstones, such as insects in amber, or they are common to a variety of minerals, such as rutile needles. Many jewelers and buyers consider them to be flaws, and they are removed or “hidden” during the cutting of the stone to produce a clean gem. However, inclusions can be advantageous, as well as fascinating, and they do have their uses.

Indicolite (tourmaline) The gemstone is blue and bi-colored, so it’s from a parti-colored crystal. It weighs 51 carats and is long and narrow. The stone has two different color directions, making it pleochroic.

Indicolite (tourmaline)
The gemstone is blue and bi-colored, so it’s from a parti-colored crystal. It weighs 51 carats and is long and narrow. The stone has two different color directions, making it pleochroic.

Inclusions, such as peridot “lily pads,” sunstone platelets, hexagonal zoning in Corundum, and “horsetail” (asbestos fiber) inclusions in demantoid garnets, can be used to establish the identity of a gemstone. They prove that a stone is natural and has not been heated; small crystals and rutile needles in ruby and sapphire alter during heat treatment.

Tanzanian natural rubies Red with a hint of blue, these stones are small at 1.05ct each. Possible stones include garnet, ruby, or rubellite, but garnet and rubellite are not quite this color and are larger.

Tanzanian natural rubies
Red with a hint of blue, these stones are small at 1.05ct each. Possible stones include garnet, ruby, or rubellite, but garnet and rubellite are not quite this color and are larger.

Inclusions can prove that a stone is not a synthetic or an imitation. For example, the inclusions of a natural emerald are different from those in a synthetic emerald.

Faceted emerald This Colombian emerald has small, jagged three-phase inclusions consisting of liquid, gas bubble with crystal element (commonly pyrite).

Faceted emerald
This Colombian emerald has small, jagged three-phase inclusions consisting of liquid, gas bubble with crystal element (commonly pyrite).

And, lastly, inclusions can indicate a source, which can be a huge bonus in selling a gemstone. For example, Burmese rubies typically contain rutile needles, while Brazilian Paraiba tourmalines can have copper inclusions, which are not found in other tourmalines. Colombian emeralds can have pyrite crystals and a rare trapiche formation; Sri Lankan spinel contains zircon crystals; and peridot from Pakistan can be identified by black Ludwigite needles. –Judith Crowe

Parti-colored stone A watermelon tourmaline pear-shaped pendeloque. Certain minerals, such as watermelon tourmaline, ametrine, and sapphire, occur as parti-colored crystals.

Parti-colored stone
A watermelon tourmaline pear-shaped pendeloque. Certain minerals, such as watermelon tourmaline, ametrine, and sapphire, occur as parti-colored crystals.

Learn More About Gemstones

With a glossary, “charts, timelines, illustrations, and photography to help you identify different gemstones and demonstrate how they can be used in different designs and settings,” the information in Gemstones: A Jewelry Maker’s Guide to Identifying and Using Beautiful Rocks will help you add color, interest, and value to your designs using the most appropriate stones.

You can discover which stones are typically not suited for knockabout jewelry like rings and bracelets. Likewise, see which gems are better suited for gently worn jewelry like earrings and pendants—and why. Learn about sources of gems (both mining and purchasing), gemstone phenomena, pricing and grading, treatments, and so much more! Every gem lover and jewelry maker should have this book at hand.

All photos by Phil Wilkins, from the book Gemstones: A Jewelry Maker’s Guide to Identifying and Using Beautiful Rocks by Judith Crowe. Copyright © 2019 Quarto Publishing plc, an imprint of The Quarto Group


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