Agate Value, Price, and Jewelry Information

Agate, Mexico, “Fortification Agate” (a picture agate with a pattern that resembles a fortress), Slab ~ 4 inches across. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Agate is a variety of chalcedony, a cryptocrystalline form of quartz. Translucency, patterns of color, or moss-like inclusions may distinguish this stone from other forms of chalcedony. Agates can show a wide variety of vivid, multiple colors. These are principally the result of traces of oxides of iron, manganese, titanium, chromium, nickel, and other elements. All agates take a wonderful polish and are tough enough for most jewelry uses. Designers often take advantage of the intriguing patterns these stones have to offer to create unique and fascinating pieces.

Agate Value

In general, agate values are quite modest. Their prices reflect mainly labor and artistry rather than the value of the material itself. Agates of large size or with particularly distinctive, fine, or landscape-like color patterns are at a premium. Custom cut pieces or stones from collectible locations would be substantially more expensive.

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Agate Value via Gem Price Guide

Cabochons	All Sizes
Agate	$.50 to /ct
Fire Agate	to /ct
Blue Chalcedony	to /ct

See the entire Gem Price Guide.

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Agate Information

Data	Value
Name	Agate
Is a Variety of	Chalcedony
Varieties	Fire Agate, Iris Agate
Crystallography	Hexagonal, cryptocrystalline
Refractive Index	1.530 to 1.543
Colors	All
Luster	Greasy, waxy
Polish Luster	Greasy to vitreous
Fracture Luster	Dull to waxy
Fracture	Uneven
Hardness	6.5 to 7
Toughness	Good
Specific Gravity	2.60 to 2.64
Birefringence	Up to 0.004
Cleavage	None
Dispersion	None
Luminescence	Fluorescence varies with bands. Somewhat strong: yellow, blue-white
Enhancements	Dyeing (common, stable).
Transparency	Usually translucent. Occasionally transparent or opaque.
Absorption Spectrum	Dyed green gems show weak lines at 6450 and 6700 nm. Others not diagnostic.
Phenomena	Iridescence
Formula	SiO₂
Etymology	From the Ancient Greek Achates, the name of a river in southwestern Sicily where the material was found.
Occurrence	Nodules

Varieties of Agate

The color patterns in agates usually take the form of flat or concentric layers or bands. Mossy or dendritic inclusions can sometimes create the impression of vegetation and landscapes. Varieties of this gemstone are described by their color patterns, inclusions, or source.

Banded

With regular color layers and bright colors, this variety is one of the most popular. These stones are found all around the world, but Brazil is one of the most productive sources. Many of the richly colored, banded agates you see for sale are dyed.

Moss, Plume, and Dendritic

These stones contain mossy inclusions of mineral oxides that may be any color. Stones that present plant-like patterns are called moss agates. Those with feather-like patterns are called plume agates. Those with tree-like, branching patterns are called dendritic agates.

“Moss Agate” by Nicole Pellegrini is licensed under CC By 2.0 — “Moss Agate 3” by Nicole Pellegrini is licensed under CC By 2.0

Picture or Scenic

Some inclusions can create the appearance of whole landscapes, complete with lakes, shorelines, trees, and shrubs, within an agate. Stones that show these “natural pictures” are treasured.

Fire

Inclusions of plate-like crystals of limonite make fire agates iridescent. Cutting and polishing can enhance this effect.

Lace

Noted for their delicate designs, these stones are banded with intricate swirls and loops. Mexico is one of the premier sources of this material.

Iris

These stones show iridescent colors reflecting from between the color layers.

Shell

Embedded, silicified shells create patterns in these agates. Turritella agate is composed mostly of shells and shell fragments of the gastropod turritella and certain other species.

Petrified Wood

Fossilized ancient tree trunks and limbs may have their organic components replaced by agate stone over millions of years. In some cases, their woody structure may also be preserved and visible with a microscope. The agate’s color may be very bright and strong.

Synthetics

For information on synthetic quartz in general, consult the quartz gem listing.

Enhancements

Dyeing is an ancient and common practice for enhancing agates. (Chalcedony stones are relatively porous). This is usually a stable process.

A celebrated secret process for dyeing agates was developed in Idar-Oberstein, Germany, in the 19^th century. When the agate deposits in this town were depleted, emigrants to South America shipped grey agates back to Idar-Oberstein. These pieces were dyed and the results were extraordinary.

Dyeing enhancements should be disclosed to consumers.

agate in various colors — Polished, commercially dyed agate stones. “Agates Varying Colours” by Teerui. Public Domain.

Sources

Moss agates: India; Scotland; United States Northwest.
Scenic agates: Yellowstone National Park; Wyoming; Montana.
Banded agates: Brazil; Uruguay; Madagascar; Mexico; United States.
Lace agate: Mexico; Arizona; Namibia.
Fire agates: Mexico.
Petrified wood: Arizona; New Mexico; California; Washington; Oregon; various European countries; many other localities.