Agate Buying Guide


agate buying - dendritic agate bracelet with pearls
Bracelet with a dendritic agate evoking a fall scene, with 8.5 mm cultured pearls. © Linda Allen Jewelry. Used with permission.

Decorative, patterned forms of agate are excellent natural gems. This variety of chalcedony takes on a number of forms, most commonly banded with color, but sometimes with lovely inclusions that look like moss, trees, or even entire landscapes. Agate, the alternative birthstone for Geminis, is affordable even in large sizes. It can be used for jewelry or to make decorative items. Before your next agate buying trip, learn more about the rare and beautiful forms of this gem material.

Agate Buying and the Four C’s

The IGS agate value listing has price guidelines for agate, fire agate, and blue chalcedony cabochons.

Color

Agates form in a wide variety of colors due to trace metals in the mineral’s chemical makeup. Vivid natural colors in agate will have a higher value than colors that are less intense or artificially dyed. Blue and green hues are the least common. They will command somewhat higher prices than red and yellow colors.

agate buying - fairburn agate
Agates from the town of Fairburn and neighboring areas in South Dakota are known for vibrant colors and beautiful banding. “Fairburn Agate 3” (ultimately derived from the Minnelusa Formation, Pennsylvanian-Permian; collected in national grasslands east of the Black Hills, western South Dakota, USA) by James St. John. Licensed under CC By 2.0.

Clarity

Most agate is translucent, with a few transparent or opaque specimens.  Still, the gem should be eye-clean, without large inclusions or fractures.

Moss, dendritic, and plume agates are the exception. Here, the inclusions create beautiful natural patterns, the hallmark features of these stones.

agate buying - dendritic agate pendant with cognac diamonds
Dendritic agate pendant, 1 3/4 inch diameter. Accented with cognac diamonds. © Linda Allen Jewelry. Used with permission.

Cut

Agate cabochons or slices should attractively showcase the stone’s patterns. A proper cut will enhance the banding or inclusions to create a beautiful and appealing piece.

For carved or sculpted pieces, creative use of the natural patterns is most important. Accordingly, the artistic use of agate will add a premium to this gem’s cost. (Most of the expense is due to artistry and skill rather than the stone itself).

agate buying - cameo_ring
Agate gladiator cameo ring, dated 1872. © The Parisian Flea of Hampden. Used with permission.

Carat

Found in all sizes, agate prices aren’t dependent on carat weight. In fact, agate slices the size of small tabletops are commercially available.

Varieties

Because of the wide array of natural patterns, there are many different varieties of agate. Some of the more popular varieties for jewelry use are described here.

Banded Agate

Most agates have bands or concentric circles of color. Those with several different vibrant colors can be stunning, but these often arise from artificial dyes.

agate buying - banded agate butterfly
Banded agate creatively cut into a butterfly shape. “Chelyabinsk Butterfly” by Kevin Walsh. Licensed under CC By 2.0.

Fire Agate

With iridescence due to limonite inclusions, fire agates earn their name. Mined in Mexico and the southwestern United States, this gem often forms in a botryoidal habit, resembling grapes. One of the rarer forms of agate, this material is more expensive than other varieties, though still quite affordable.

agate buying - fire agate ring
Botryoidal fire agate set in a ring. “Fire Agate Ring,” commissioned by Bill Damron, fire agate set in 18k gold, hand-engraved flame design on Continuum silver ring, by Jessa and Mark Anderson. Licensed under CC By 2.0.

Moss, Dendritic, and Plume Agates

Some agates contain attractive patterns of inclusions. Moss agates are one of the most sought-after varieties, with green inclusions that resemble moss. Similarly, dendritic agates have tree-like inclusions. Inclusions that resemble plumes or feathers give plume agates their name.

agate buying - moss pendant
Moss agate pendant in 18k gold. © The Parisian Flea of Hampden. Used with permission.

Lace Agate

With delicate swirled bands, the patterns of lace agate are mesmerizing.  When properly cut, this variety gains an exquisite beauty. Red layers are considered rare in lace agate.

agate buying - lace agate
“Crazy Lace Agate (Mexico)” by James St. John. Licensed under CC By 2.0.

Scenic Agate

Certain agates can showcase patterns that resemble scenes. For example, you might see snowy mountaintops, trees, and shorelines in these rare stones. Arguably, these make the loveliest, statement piece agates.

agate buying - dendritic agate pieces
Dendritic agates resembling trees reflected in a lake are often called scenic agates or picture agates. © Linda Allen Jewelry. Used with permission.

Agate Fossils

Petrified wood made of agate can be bright and colorful. In some cases, the original tree rings are visible with little magnification.

Silicified shells are another form of agate. “Turritella agate” is comprised of gastropod shells, commonly, but not necessarily, of the genus Turritella.

agate buying - turritella
“Turritella Agate 1” (chertified fossiliferous lacustrine limestone), Laney Member, Green River Formation, Middle Eocene; North Barrel Springs Draw, south of Wamsutter, Wyoming, USA  by James St. John. Licensed under CC By 2.0.

Treatments

Dyes often embellish the color of an agate. Although dyed specimens are less valuable than their natural counterparts, the dyes are generally stable and can create a desirable color scheme for decorative items.

agate buying - dyed pendant
Dyed lace agate in a pendant. “Final Class Project” by Lee. Licensed under CC By-ND 2.0.

About the author
Addison Rice
A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club. When she isn't writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
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