Gem Profile- Chalcedony

by Judy Ellis

Chalcedony used to be considered a fibrous variety of quarts. However, it has been shown to contain quartz as well as moganite, a different form of silicon dioxide with a crystal structure unlike quartz (named for Mogan on the Canary Islands). However, you will still see various sources say that chalcedony is a form of quartz, and that agate is a form of chalcedony. They all are made up of silicon dioxide.

Chalcedony (kal-SED-uh-nee) is a quartzlike mineral, typically ranking a 7 on the Mohs scale.

This material has been used in carvings since before Roman times; Roman carved seal rings made of chalcedony remain in good condition today.

The gemstone trade refers to the gray, white, or blue translucent form as chalcedony.

The AGTA also includes this material among "Sky Blue" gems.

However, chalcedony naturally appears in virtually any color, including yellow, orange, red, pink, purple, green, black, and multicolored or banded forms.

Colored varieties of chalcedony usually have their own trade names, such as Tigerseye, Aventurine, and Bloodstone.

Joan Madouse crafted this chalcedony druzy pendant using silver-filled wire. She accented the piece with a blue briolette bead.

Blue Chalcedony has become very popular recently. It is often named for its origin, such as Mohave Blue Chalcedony from California and African Blue from Namibia.

The blue color may contain pink or gray hues, and sometimes exhibits a slight adularescence, similar to moonstone.

Bluish chalcedony from Oregon is distinct. It often features slight bands or clouds of pink, creating a lavender color, and is confusingly called Holly Blue.

Holly Blue is usually grouped with the blue chalcedonies and is typically considered the most valuable type.

Color differences in chalcedony are due to metallic impurities present during crystallization. These impurities can include elements like titanium, copper, nickel, and iron.

For instance, the Granny Smith apple-green variety, Chrysoprase, gets its vivid color from nickel.

Chalcedony is typically cabbed, carved, or made into beads. Highly transparent pieces are sometimes faceted.

Joan Madouse crafted this chalcedony druzy pendant using silver-filled wire. She accented the piece with a blue briolette bead.

White, blue, and gray chalcedony is primarily found in the deserts of California and Nevada, as well as in India, Siberia, and Iceland. However, it is also sourced from many smaller locations worldwide.

The AGTA recommends that you rinse natural chalcedony with mild dish soap and allow it to air dry. It requires no special care.

Chalcedony does not typically react to heat, though sometimes the stone is dyed or stained to enhance its color.

Glass is often used as an imitation of chalcedony. You may spot tiny bubbles, swirl marks, or "too-perfect" inclusions that indicate the true glass nature of the fake gemstone.

Gem Profile- Chalcedony

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