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Amazingly (Deeply) Tenebrescent Marialite (Scapolite), w/ Sodalite, Phlogopite from Afghanistan

7.3.2017

Amazing tenebrescence (rapid change - both darken and fade), phosphorescence, bright fluorescence.  If I am correct on my analysis of this specimen (and I believe that I am) this is a major discovery (for me).  Read more below the pics...

 

There’s a lot of confusion about the minerals from Afghanistan.  Sodalite, afghanite, hauyne, scapolite, lapis, on and on....  They are all interrelated and easily mistaken for one another.  The scapolites are often munged.  Sometimes they are called wernerite, other times scapolite, and even other times misidentified as sodalite/hackmanite.  Wernerite is an obsolete name used to describe a member of the scapolite group.  So far, all of these crystallized specimens appear to be marialite, a member of the scapolite family - so that’s what I’m gonna call it.

 

This is a mass of very tenebrescent marialite crystals on the first side, very fluorescent under LW.  Under shortwave they start out fluorescing a bright yellow (almost as good as LW) but as the tenebrescence sets in the fluorescence dulls as shown in the SW pic.  The tenebrescence is a deep blue rather than purple as in the hackmanite from this area. It fades quickly (seconds), unlike the hackmanite from Afghanistan which can take days to fade.  

 

There is some question regarding irradiation of these pieces.   One study quoted by Howie G noted "that irradiation changed the tenebrescent properties of colorless scapolite but not the fluorescent properties. However, radiation did not change the daylight properties either; the colorless scapolite remained colorless after the irradiation. Although it certainly is common to find that gemstones are irradiated, there is apparently no easy way to determine whether the day light purple scapolite has been irradiated or not. Another words purple scapolite in daylight that has not been irradiated does exist, as does colorless scapolite from Afghanistan that has been irradiated"

 

This is one of only a couple of pieces I have seen with these characteristics.  I’ve seen quite a few pieces from Afghanistan but none are tenebrescent like this - does this mean they are rare?  Maybe, or maybe no one is focusing on this trait.  The reverse side shows massive sodalite (hackmanite) which is both tenebrescent and very phosphorescent.  The tenebrescent color of the sodalite is the typical purple and takes forever to fade.

 

I am but a lowly glowhound and am the first to admit that I come up with wild theories.  But I am often proven correct and I think I’ve nailed this one.  But I have also been proven wrong many times, so take my analysis with a grain of salt:

 

My theory about this rock (and others like it): This piece fluoresces a bright yellow under LW, deepens to a deep blue (tenebresces) after exposure to SW (and fades back in seconds upon exposure to white light), has obvious purple tenebrescent sodalite on the back with phosphorescence and white fluorescence SW.  The crystals I am calling scapolite/marialite exhibit a schiller effect as described below.  All of this indicates that the yellow fluorescing minerals are not sodalite.  Their habit matches pieces of scapolite I have seen from the area.  I believe they are scapolite/marialite.

 

 

Below is an excerpt from the GIA website:

 

“Tenebrescent scapolite from Afghanistan. At the 2004 Tucson Gem shows, gem and mineral dealer Herb Obodda (H. Obodda, Short Hills, New Jersey) showed GIA personnel several rough and cut pieces of a colorless gem material from Badakhshan, Afghanistan, that was thought to be hackmanite on the basis of its reversible photochromism (or tenebrescence, a property in which some minerals darken in response to radiation of one wavelength and then reversibly lighten on exposure to a different wavelength). When “charged” under Mr. Obodda’s strong UV source, the stones turned blue. When they were exposed to daylight or a strong incandescent light source, the color faded completely in seconds. Mr. Obodda obtained the rough material during buying trips to Pakistan in early 2003 through early 2004. He said that the local dealers have habitually referred to the colorless sodalite from Badakhshan as “hackmanite”— even though they were unaware that any of the pieces showed tenebrescence. When he returned home and tested the initial parcel with a UV lamp, Mr. Obodda was pleased to find that a few pieces showed tenebrescent behavior. He also noted a subtle but distinctive feature that could be used to differentiate the tenebrescent stones from the other material in the parcel in the absence of a UV lamp: They showed a schiller effect when viewed with a strong pinpoint light source in certain orientations. Hackmanite, a sulfur-rich variety of sodalite, was first discovered in Greenland in the early 1800s. A mineralogical curiosity, it can be made to change repeatedly from light yellow to pink when alternately exposed to sunlight and UV radiation (see, e.g., Summer 1989 Gem News, pp. 112–113). The coloration of this Afghan material was much different, however, in that it changed from colorless to blue on exposure to UV radiation.  Mr. Obodda loaned four rough pieces (13.37–55.54 ct) and 14 faceted examples (0.17–5.17 ct) of the tenebrescent material to GIA for examination. He also donated some rough fragments to the GIA Collection. Gemological testing of four of the cut stones (0.91–5.17 ct) revealed consistent properties: R.I.’s—1.536 and 1.541, S.G.—2.58, and yellow-orange fluorescence to UV radiation (strong to long-wave and weak to short-wave). Hackmanite is optically isotropic with an R.I. of 1.483, whereas the properties of the four samples are consistent with those of scapolite (this identity was confirmed by Raman spectroscopy). When viewed with a gemological microscope, all four stones exhibited dense parallel stringers throughout (figure 15), and some contained planar clouds or “fingerprint” inclusions. The schiller effect noted by Mr. Obodda is caused by reflections from these features when viewed with a strong pinpoint light source (figure 16). When the samples were exposed to short-wave UV radiation, with the 4-watt lamp positioned nearby for approximately one minute, they changed from colorless to deep blue. The larger stones showed this effect more dramatically. Shorter exposure times also produced the blue color, but it took at least a full minute to get a saturated blue. Long-wave UV radiation also produced this color modification, but the achieved color was not as saturated. The color was stable as long as the stones were kept in a dark or dimly lit room, but they began to fade as soon as they were exposed to light (much faster in incandescent than in fluorescent light). In fact, an intense incandescent light source caused their color to fade completely in a few seconds. The color modification was repeated on one stone at least five times, and each time the results were the same. A brief video showing the reversible color change is available online in the G&G Data Depository at www.gia.edu/gemsandgemology. Quantitative chemical analyses were obtained by one of us (GRR) using an electron microprobe on a polished fragment of the scapolite. The average formula derived from three analyzed points was Na4Al3Si9O24Cl0.9S0.09; traces of carbonate may also be present but could not be analyzed by this instrument. The formula shows that the scapolite species is marialite, with a minor sulfide component. Sulfide photochemistry is what produces the blue color of lapis lazuli and red coloration in hackmanite and tugtupite. Mr. Obodda also loaned one rough sample that was representative of the non-tenebrescent material in the parcels he purchased in Pakistan. Preliminary Raman analysis was indicative of quartz. In addition, Mr. Obodda has faceted colorless sodalite that was reported to be from the same mining area in Badakhshan. Some purple sodalite from Badakhshan also shows tenebrescence, changing from “pale lilac/magenta in artificial light to a deep purple/magenta in sunlight” (T. Moore, “What’s New in Minerals,” Mineralogical Record, Vol. 33, No. 1, 2002, pp. 97–98). It should also be mentioned that purple scapolite has been produced recently from the same area of Badakhshan, but it does not exhibit tenebrescence. During his August 2005 buying trip to Pakistan, Mr. Obodda could not find any more of the colorless “hackmanite” in the marketplace. So far, he estimates that he has cut approximately 20 stones weighing less than 1 ct, a dozen weighing near 1 ct, and 10 stones in the 5 ct range; the largest stone weighed 6.7 ct. To the best of our knowledge, tenebrescence has not been reported previously in scapolite. In addition to hackmanite, only a few other gems show this feature, such as spodumene (E. W. Claffy, “Composition, tenebrescence, and luminescence of spodumene minerals,” American Mineralogist, Vol. 38, 1953, pp. 919–931) and tugtupite (A. Jensen and O.V. Petersen, “Tugtupite: A gemstone from Greenland,” Summer 1982 Gems & Gemology, pp. 90–94).”

 

Naming scapolites per the MNMMN:


In order to eliminate the confusion in the scapolite nomenclature, the CNMMN has approved in 1986 the proposals as follows: (a) the name scapolite should be retained as a group name to encompass minerals in the marialite meionite series; (b) the names of marialite (Na4AlaSi9024CI) and meionite (Ca4A16Si6O2r be given species status; (c) the names of dipyre and mizzonite be regarded as varietal names; (d) the name wernerite be discarded as being synonymous with scapolite.

 

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