Sphalerite or not? Part II
Sphalerite in quartz?
Tower number 3 is mainly white with brown-black non-transverse bands referred to as “sphalerite”. However, the brown-black bands have a Mohs hardness of about 6 – 7 and are thus harder than sphalerite (Mohs 3½ -4). Possibly the sphalerite here is then in quartz, but this cannot be determined without additional research. In any case, the white in this tower is clearly quartz, between which a constituent fluoresces yellow-white with UVA. Chemical analysis (EDX) in a lab shows no zinc and/or sulfur (the constituents of sphalerite) to be present in the brown-black parts. However, quartz was detected with traces of manganese; the amount of manganese was too small to determine which mineral was involved (probably a manganese oxide). It did not become clear what causes the fluorescence.
Tower 3 with “bands of sphalerite” appears to be quartz with inclusions of manganese
Purple sphalerite?
Tower 4 consists of a purple-black mottled rock and is therefore sold under the name “purple sphalerite” or “purple druzy sphalerite”. Examination under the microscope clearly reveals purple cubic crystals, probably fluorite. The purple constituents fluoresce red under UVA. The hardness also fits fluorite (Mohs < 5), but would also fit sphalerite, although I know of no purple cubic sphalerite. In any case, quartz crystals are also clearly recognizable in the cavities. Here and there, small yellow-brown spots can be seen, could that be the sphalerite? Or still the black component in this tower? Without further analysis I unfortunately could not determine that.
In the laboratory, chemical analysis (EDX) supplemented by Raman spectroscopy identified three other minerals in addition to the quartz. The purple crystals are indeed fluorite, the yellow-brown spots are muscovite (mica) and the black mass appears to be graphite. Thus, no trace of sphalerite can be found in this tower either.
Tower 4 with “purple sphalerite” turns out to be purple fluorite, white quartz, muscovite and graphite
Conclusion
Sphalerite or not? Not. Unfortunately, I found out that sphalerite has not been identified in any of the 4 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.
Read PART I here.
Would you like to learn to recognize or identify minerals based on their characteristics? Perhaps the online basic course in mineral identification is something for you!
Of course you can also contact Stapel van Stenen for advice or analysis of minerals.
Responses