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Tschermakite
A valid IMA mineral species
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![◻(Ca2)(Mg3Al2)(Al2Si6O22)(OH)2](#"/photo-249441.html"><img src="/image.pl?url=https%3a%2f%2fwww.mindat.org%2fimagecache%2f4a%2f58%2f02790010017271927243006.jpg&f=jpg&w=240" alt="02790010017271927243006.jpg" /></a><div><b>Gustav Tschermak von Seysenegg</b></div></div></div><div><div><span>Formula:</span><div class=){kind=link}
Name:
Named in honour of Gustav Tschermak von Sessenegg (19 April 1836, Littau, Moravia (now Czech Republic) - 4 May 1927, Vienna, Austria), Austrian mineralogist at the University of Vienna. He specialized in silicate minerals and meteorites. He established the journal Mineralogische und Petrographische Mitteilungen (Mineralogical and Petrological Reports). The mineralsilvialite is named after his daughter.
Tschermakite is defined as a Tschermakite Group member with Mg>Fe2+ and Al>Fe3+ in the C position. Tschermakite has been redefined in the 2012 Amphibole nomenclature in that:
1) The formula is changed from ☐(Ca2)(Mg3AlFe3+)(Al2Si6O22)(OH)2 to ☐(Ca2)(Mg3Al2)(Al2Si6O22)(OH)2. Consequently all pre-2012 literature references to tschermakite should be checked to verify that Al>Fe3+ in the C position. If Fe3+>Al in the C position the material will be ferri-tschermakite.
2) The tschermakite group is in the 2012 nomenclature defined with C(Al+Fe3++2Ti)> 1.5 apfu, whereas the pre-2012 definition was defined with 5.5 < Si < 6.5 apfu. This redefinition does not change the formula, but many amphiboles qualifying as tschermakite pre-2012 will now be ferro-hornblende or ferro-ferrihornblende.
It should also be noted that pre-1978 tschermakite was defined with A+B(Na+K+Ca)<2.5. As tschermakite often contains less than 2 apfu Ca, older literature may describe amphiboles with A(Na+K)>0.5 as tschermakites. These are now considered pargasites.
NOTES:
- Amphiboles fromLongido District, Arusha Region, Tanzania are still erroneously labeled tschermakite or alumino-tschermakite. The identification of these amphiboles as pargasite are well documented by Simonet, Cedric (2000) and others.
- The tschermakite end-member composition is unstable, and most analyzed samples are close to one or more of the tschermakite/hastingsite/pargasite/sadanagaite joins. Any tschermakite specimen should therefore be analysed with qualitative chemical analysis (EMPA minimum, ideally in combination with Mössbauer spectroscopy).
1) The formula is changed from ☐(Ca2)(Mg3AlFe3+)(Al2Si6O22)(OH)2 to ☐(Ca2)(Mg3Al2)(Al2Si6O22)(OH)2. Consequently all pre-2012 literature references to tschermakite should be checked to verify that Al>Fe3+ in the C position. If Fe3+>Al in the C position the material will be ferri-tschermakite.
2) The tschermakite group is in the 2012 nomenclature defined with C(Al+Fe3++2Ti)> 1.5 apfu, whereas the pre-2012 definition was defined with 5.5 < Si < 6.5 apfu. This redefinition does not change the formula, but many amphiboles qualifying as tschermakite pre-2012 will now be ferro-hornblende or ferro-ferrihornblende.
It should also be noted that pre-1978 tschermakite was defined with A+B(Na+K+Ca)<2.5. As tschermakite often contains less than 2 apfu Ca, older literature may describe amphiboles with A(Na+K)>0.5 as tschermakites. These are now considered pargasites.
NOTES:
- Amphiboles fromLongido District, Arusha Region, Tanzania are still erroneously labeled tschermakite or alumino-tschermakite. The identification of these amphiboles as pargasite are well documented by Simonet, Cedric (2000) and others.
- The tschermakite end-member composition is unstable, and most analyzed samples are close to one or more of the tschermakite/hastingsite/pargasite/sadanagaite joins. Any tschermakite specimen should therefore be analysed with qualitative chemical analysis (EMPA minimum, ideally in combination with Mössbauer spectroscopy).