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Gaspeite: The Fluorescent Pretender

12.4.2015

I’ve known more than one collector who has been enticed by the brilliant blue/green fluorescence of the mineral gaspeite.  In fact, under the light of a Convoy S2+ long wave flashlight, this material can produce one of the brightest fluorescent responses of any mineral; it’s nearly blinding!  The only problem is that gaspeite is not fluorescent.  So what’s going on here?  Read on to find out.

 

Named after its type location, the Gaspé Peninsula in Québec, Canada, gaspeite is a relatively rare nickel carbonate mineral having the chemical formula (Ni,Mg,Fe)CO3.  Due to its apple green color, it is often used as a lapidary material.  Looking at its chemical structure, there is nothing present that would serve as an activator of fluorescence, and the iron component would act as a quencher of fluorescence.  The following photograph shows a typical specimen of gaspeite.

Figure 1.  Gaspeite specimen from Australia, seen under visible light.  The lovely apple green color of this mineral makes it a popular material for lapidary and gemstone use.

 

As seen in the next photograph (Figure 2), the same specimen shows a brilliant blue/green fluorescent response under long wave UV (365nm).

Figure 2.  The same gaspeite specimen shown in Figure 1, displays a brilliant blue/green fluorescent response under an 18 watt long wave UV source.

 

As seen in Figure 3, below, this piece also shows a similar, but less bright fluorescent response under short wave UV (254nm).

Figure 3.  The short wave UV response of this specimen is similar to that seen under long wave, but is less intense.

 

So what’s responsible for the brilliant fluorescence under UV if gaspeite is not a fluorescent mineral?  As mentioned above, gaspeite is often used as a lapidary material, as this green mineral takes a high polish and makes beautiful inlays and cabochons in jewelry, and it is this use as a gemstone that provides a clue to the nature of its fluorescence.  Figure 4 shows an example of the use of gaspeite as a gemstone.

                                                 Figure 4.  This  ring features a gaspeite cabochon in a sterling silver setting.

 

Having a hardness of only 4.5 – 5 on the Mohs scale, gaspeite is a relatively soft material and it can also be somewhat brittle.  These characteristics can make the native mineral difficult to work with for lapidary applications.  As is often done with turquois and other soft gemstone materials for the same reason, gaspeite is sometimes treated with a resin-based stabilizing agent to make the material more durable and less prone to fracturing during the lapidary process.  Some of the resins used for this purpose are brightly fluorescent under UV after they have hardened.  Thus, the mystery of fluorescence in gaspeite is solved.  It is not the mineral itself that is fluorescent, but in fact is the resin that is used to stabilize the mineral.  The following photograph shows a piece of untreated, native gaspeite.

Figure 5.  A piece of native, untreated gaspeite from Australia, seen under visible light.

 

As seen in Figure 6, below, under UV, the same specimen shows no fluorescent response.

Figure 6.  Same specimen of untreated gaspeite shown in Figure 5, photographed under an 18 watt long wave UV source.  The untreated material shows no fluorescence under UV.

 

Resin-stabilized gaspeite often has a more glossy, almost wet looking appearance than the untreated mineral.  As can be seen in the following photograph, this difference is obvious when treated and untreated gaspeite are compared side by side.

Figure 7.  Side by side comparison of resin-stabilized gaspeite (left) and native, untreated gaspeite (right).  Note the more saturated color and wet look of the resin-stabilized material on the left.

 

As shown in Figure 8, below, the difference between these pieces is striking under long wave UV.

Figure 8.  Side by side comparison of the long wave fluorescent response of the same two specimens shown in Figure 7.  Resin-stabilized gaspeite is at left and untreated gaspeite is on the right.  This photograph was taken under an 18 watt long wave UV source with a low level of ambient white light to dimly outline the non-fluorescent native gaspeite at right.

 

Due to its relative rare occurrence and use as a gemstone, gaspeite can be an expensive mineral, and for the same reason can be an expensive mistake for the uninformed fluorescent mineral collector.  I personally know of several collectors who thought they had discovered a prize fluorescent mineral find and purchased a costly gaspeite specimen, only to find out later that the brilliant fluorescence under UV was due to the treatment of the material, and not the mineral itself.  Treated gaspeite appears to be a worthy fluorescent mineral, but in fact is only a pretender.

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