Ammolite Buying Guide

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With its bright rainbow play of color, ammolite is sure to draw attention. Once worn by members of the Blackfeet tribe to aid in hunting buffalo, this gem is a newcomer to the world jewelry market. Ammolite is the gem-quality aragonite shells of ancient ammonites, a mollusk which thrived on the bottom of the sea covering much of America 70 million years ago. Now found in the Bearpaw formation of the Rocky Mountains, these shells were preserved as the beautiful gem material we know today. After entering the market in 1969, ammolite became an official organic gemstone in 1981.

Learn about this unique gem’s quality factors before embarking on your next ammolite buying trip.

Ammolite Buying and the Four Cs

Although ammolite grading differs from other colored gemstones, the four Cs still prove useful for understanding ammolite quality.

The IGS ammolite value listing has price guidelines for ammolite naturals, doublets, and triplets.

Color

Color is the most important factor in ammolite quality. Higher quality ammolite exhibits more, brighter colors, greater iridescence, shifting color with different viewing angles, and color regardless of the gem’s rotation.

Number and Rarity of Colors

Ammolite can display any color of the rainbow, but specimens that display three or more colors are the most desirable.

Red and green hues are common, while blue, violet, gold, and crimson are rare.

Iridescence

Ammolite’s unique structure allows for beautiful iridescence. In this gem, tiny aragonite crystals align in a plate-like structure whose thickness is near the wavelength of white light. Because of this, a mesmerizing play of color appears in the stone. Ammolite with greater iridescence will have more value.

Chromatic Shift

As a piece of ammolite rotates, an observer can witness changing colors. Lower-quality ammolite is monochromatic, meaning a slight change, perhaps from a lime green to a more pure green. Mid-grade ammolite will exhibit a more drastic change, perhaps from red to yellow. This is known as dichromatic. Top-quality gems have a spectrochromatic shift, showing strong color changes and a plethora of intermediate hues.

Viewed from different angles, this ammolite specimen shifts hues from predominantly yellow and orange to green with streaks of blue. Slide show photos 1, 2, 3, and 4 by David Abercrombie.  Licensed under CC By-SA 2.0. (Slide show created to highlight chromatic shift).

Rotational Range

High-quality specimens have strong color regardless of viewing angle. However, most ammolite doesn’t show iridescent color at all angles. Instead, organic material inhibits light diffraction. Thus, at certain angles, most gems appear grey or black.

Clarity

Sheet ammolite, or ammolite without fractures or cracks, is the most valuable variety. However, most ammolite has patterns of cracks. These patterns have descriptive names, like “dragonskin,” “feather,” or “cobblestone.” Some collectors seek out rare patterns.

Cut

Typically, ammolite pieces receive symmetrical cuts that showcase relatively symmetrical colors. Consumers generally prefer standard shapes, such as ovals and rectangles, rather than off-shape pieces. However, with this unique gem material, asymmetrical and modern jewelry design can create very attractive alternatives. Freeform shapes can fetch a good price, especially with proper design. For example, matching asymmetrical stones could be arranged as butterfly wings.

Carat

While visual size is more important than carat weight, some ammolite is priced per carat. For such pieces, the natural backing of the stone shouldn’t exceed 1.5 mm. Of this 1.5 mm, gem-quality ammolite is generally 0.1 – 0.3 mm thick after polishing.

Although ammonites could grow up to 3 feet in diameter, generally only a fraction of the shell is gem quality. However, gem-grade pieces up to 6 inches across do occur. The price per carat doesn’t rise dramatically for larger pieces.

Some complete gem-grade shells make exceptional specimens. These will command good prices. Small shells can also function as fascinating jewelry items.

Grading

Although no standard grading scheme for ammolite exists, several companies have created grading schemes for this gem. (You can learn about one such system in the value section of our ammolite gem listing). When purchasing an ammolite, viewing the stone in person is the best way to assess quality. This way, you can decide for yourself which gem you’ll most enjoy.

Before purchasing ammolites online, make sure the vendor has a return policy if you’re unsatisfied with the stone’s quality. Buyer beware, especially when dealing with independent sellers. Some will advertise inflated grades in order to sell at a higher price.

Jewelry Considerations and Care

Ammolite is a soft gem, best suited for jewelry such as pendants, earrings, and brooches, where it’s unlikely to be scratched. Assembled stones, better protected from scratches, make good choices for rings and bracelets.

Prolonged exposure to sunlight can bleach ammolite, so limit daytime wear and store your ammolite away from light.

Follow the care recommendations for pearls. Store ammolite jewelry separately from harder gems and clean gently with a soft cloth. Furthermore, because aragonite is water soluble, avoid extended contact with water.

Assembled Stones

While naturals fetch the best prices, assembled stones can be just as attractive. Naturals are gem ammolites on their original shale or limestone, while assembled stones have a clear protective layer on top. Because of the hard top stone, doublets and triplets have good scratch resistance. Thus, they’re recommended for ring use. The top layer of an assembled stone may be domed or faceted for different aesthetics.

Some ammolites have very thin natural backings. These aren’t sturdy enough to form doublets. For such gems, a backing, often shale or onyx, in addition to a hard top, improves durability. These assembled stones are called triplets.

While naturals can reach the highest values, they’ll scratch easily and are best suited to mineral collections. On the other hand, doublets and triplets make more durable jewelry stones but don’t hold values as high as naturals.

Treatments

Stabilization with epoxy prevents layers from flaking. In addition to protecting the stone during wear, epoxy prevents chipping during cutting. Because this coating may wear off over time, coated gems require occasional care. Be sure to ask whether your ammolite has undergone this treatment before purchasing.