The Valuation of Fine Banded Agate Specimens

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There is no ready price reference for the valuation of fine, high-quality banded agate specimens. Unlike baseball cards or coins, no one has created a price list simply because of the nature of banded agates. Each agate is unique, so one cannot readily characterize or categorize a set of agates and establish a universal price reference tool. Additionally, the sales of agates does not occur with regular frequency at auctions, in clearing houses, or in situations where prices can be readily referenced and collected at scale.

However, certain attributes of an agate can drive its value, and these traits are recognized and sought after by collectors.

In this discussion, I attempt to describe my assessment of these valuation characteristics to help new collectors understand the reasons behind the cost of an agate. It is important to note that every agate is unique and each can be considered a work of art. Therefore, the seller can determine their price without fear of a ready price reference.

Reputable sellers will try to price banded agates based on replacement theory plus a fair margin. These larger sellers should have a good understanding of the availability of any particular agate of a similar nature and what it might cost to replace the agate they are selling.

Inventory replenishment can be done either by cutting rough or by acquiring finished agates from others at commercial events or in private sales. However, in many cases, there is no quality rough to cut or a supply of a particular agate on the market. This makes replacement pricing more difficult for the seller, who may not believe they can replenish their inventory. 

Thus, one could expect to see very high valuations in the case of very rare agates with no new supply.

When comparing the value of two agates, a good method is to examine both sides of a cut agate nodule and explain why one side may be more valuable than the other. We provide examples, photographs, and pricing on a relative scale to illustrate these valuation dynamics, with an attempt to change one attribute at a time in the agate pairs.  Where we have priced or purchased matched pairs, we will also provide pricing in USD.

Concerning the intrinsic factors, the features in the physical stone, there are many, and some of the most important are summarized herein:   

• Color and pattern:  factors that would increase the value of an agate include the precision and parallel nature of banding, whole patterns versus unbroken patterns, and contrasting banding.  Vibrant colors and other observable features and their composition within the agate also drive value.  For example, patterns that show a face or other recognizable motifs will command a significant premium over a similar agate without this feature.   

• Physical attributes: The size, dimensions, shape, and solidity of the agate will impact its valuation. Larger agates with complete patterns and no fractures can be extremely rare. A pleasing circular or oval shape is more desirable than an irregular one. Solidity refers to the amount of agate versus non-agate components within the specimen, with higher valuations for agates with more agate banding. Large hollow voids, quartz centers, calcite inclusions, and excessive host rock will lower valuations. 

• Finish: The final polish on an agate is crucial for its valuation, as an improper polish will affect its presentation. Both flat-face and domed-face polish agates exist, with higher valuations typically given to flat-polished specimens. Rounded edges resulting from the cutting process, or to continue the pattern around an edge, will decrease value. Microfractures from improper cutting, heat spots from dry polishing, and fractures generally will lower valuations.

• Agates treated in any way, for example, dyed agates or fracture-filled agates will always impact value, reduced by the extent of the treatment, which any reputable seller should always disclose.   

Extrinsic factors refer to the external factors that affect the value of agates. The most important of these factors include the relative scarcity or rarity of high-quality specimen agates (supply) and collector demand.

• The scarcity of collector-grade agates from a specific location and collector interest in that particular location can drive up value.   
• Agates with special provenance, such as those published in books, owned by prominent collectors, or displayed at shows or museums, can also gain incremental value.
• Rarity also applies to the visual and physical features of a particular agate. For example, a common Brazilian agate can be considered rare if it contains unique features such as a recognizable face, rare colors, or other atypical characteristics that collectors value.

Rarity implies limited availability, which can fluctuate due to changes in the supply. At times, new mining or discoveries can increase supply, or a new collection or stockpile of rough nodules could come to market increasing supply.  

However, truly rare agates include those whose mining localities may be closed for the foreseeable future or have been depleted. Once a deposit is exhausted, the existing agates represent all that will ever be available, potentially leading to higher prices, such as with the Arco Iris (Rainbow) Laguna Agates or the Brazilian Polyhedroid Agates.  For other agates, the supply may seem endless, such as with Lake Superior Agates or Brazilian Agates given their massive geologic deposits.   

Similar to artwork, the beauty of banded agates is subjective and depends on the perspectives of both the buyer and the seller. This discussion aims to provide insight into the characteristics that influence the value of high-quality natural and unadulterated (no dyes, no bonding agents) specimen banded agates. 

The accompanying pictures show matched pairs of agates and is intended to provide a subjective assessment of relative values, and where available prices in USD.  Over time, we will continue to add more agate pairs, changing attributes and discussing implications to value.