Sphalerite or not? Part I
Quite some time ago I received from one of my students who also sells stones a number of polished towers of “sphalerite”. At least under that name the material was sold by the wholesaler. Partly as a result of taking the course, the discerning saleswoman had questions about the identification, also because the towers look quite different and do not show clear characteristics of sphalerite. Unfortunately, it is not known exactly where the different objects came from. This material is also still widely offered over the Internet at this time, both from Indonesia and China. Hence I am sharing here my analyses of 2 of the 4 towers, the rest you can read in Part II here.
No sphalerite but goethite in quartz
In the first tower, the brown spots are referred to as “sphalerite,” but I measured a hardness of about Mohs 6 – 7, much harder than sphalerite (Mohs 3 1/2 – 4). In any case, the white in this tower is quartz, possibly the sphalerite is in the quartz then, but that cannot be determined without additional examination. However, chemical analysis in a lab shows no zinc and/or sulfur (the constituents of sphalerite) are present in the brown mass. The brown mineral has been identified as goethite, an iron oxide, often a weathering product of other iron minerals.
Purple sphalerite? definitely not
Tower 2 has gray-black bands that have a Mohs hardness of 5 – 6, making them harder than sphalerite (Mohs 3 1/2 – 4). Furthermore, overtly white/clear quartz crystals are visible and small purple crystals here and there under the microscope. Since there is also a purple-blue reaction with longe wave UV (UVA), this could be fluorite. The yellow spots effervesce with acid and give a red fluorescence with short wave UV (UVC), probably calcite. Additional examination in the lab shows that there is indeed quartz and fluorite in the tower. Unfortunately, no sphalerite was detected in the gray-black material. It was not possible to determine what mineral this is, probably manganese oxides.
Conclusion
Sphalerite or not? Not. Unfortunately, I found out that sphalerite has not been identified in any of the towers despite being sold under that name. Unfortunately, much, and perhaps more and more, material is still being offered whose identification is geologically incorrect. When a wholesaler sells it that way the incorrect name quickly spreads like an oil slick among all sellers and enthusiasts. It is good that there are more and more critical sellers like my student, who do like to sell their stones with the correct information.
Would you also like to learn to better recognize or identify minerals based on their characteristics? Perhaps the online basic course in mineral identification is for you!
Of course, you can also come to Stapel van Stenen for mineral advice or analysis.
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