Collectors of gems and minerals like knowing where their treasures originate.
Provenance is a term used to describe where a stone occurs geographically.
Often there is a monetary value associated with certain geographical locations. The finest rubies coming from the exotic location of Burma can sell for 10 times a similar Sri Lankan stone, even though visually they appear the same.
This is significant when we are looking at differences of tens of thousands of dollars per carat.
Once a gem is cut and polished, passing through numerous suppliers along the chain, provenance can become difficult to document.
Some stones might have characteristic visible inclusions, other minerals found within the stone giving a clue to where the stone started the journey.
The geological process in which some gems begin their existence can be different, giving hints as to where they were formed underground. Some of these clues can overlap into other regions, making a determination challenging.
Even going to mining areas can yield stones from other areas, synthetics and outright frauds, such as carefully fashioned glass imitations.
When money becomes an issue, the saying “buyer beware” is good advice.
As new deposits are found, scientists must carefully examine the stones to see what characteristics are shared and which are distinct.
Gem labs working on origin determination rely on careful observation as well as advanced testing utilizing a myriad of spectrometers. These commercial labs provide documentation for important and valuable stones, ensuring the consumer is protected.
Society expects a report when purchasing diamonds, and now the colored-stone market is following as well.
Why would collectors care, or more importantly, pay more, for a rock or gem from a specific area?
Sometimes, it is simply coming from an exotic enchanted land not easily accessible. Maybe there is no longer production from these places, making the stone rare and unattainable. Many fine gems and minerals come from areas of political unrest, making collecting a challenge.
As with any collection, much of the joy is in the hunt — buying the best you can afford or trying to find as many localities as possible. It is often all about the story.
Where does the UA fit in this story? As one of the top geoscience universities in the country, the University of Arizona is developing a gem science program.
This program, unique for a research university, will bridge the gap between classical mineralogy and the field of gemology where a person cuts, fashions and shapes minerals into desirable objects of beauty.
Principal areas of research will focus on the chemistry to reveal origin determination, employing a long history of advanced testing techniques.
One of the main tools is LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) to identify not only the elements but all the isotopes of the elements found in a gem or mineral. A single element might have several isotopes or forms that can be used to identify geographical or geological sources.
Geosciences professor George Gehrels is conducting an exploratory study on Tsavorite garnet, a beautiful green variety from Kenya and Tanzania. The range of color for these stones can be due to a combination of several elements: chromium, vanadium, iron, titanium and manganese.
Working with an artisanal miner to obtain samples, the hope is to identify ratios that cause different shades of color as well as specific locations based on the color elements.
Each color hue has a separate value, and the location adds to the romance for the consumer. The chemical makeup of gem materials is responsible for color, and consumer demand relates to which color is most valuable.
Stay tuned as our story unfolds.