Tschermakite (original) (raw)

Formula:

◻(Ca2)(Mg3Al2)(Al2Si6O22)(OH)2

Colour:

Medium green to dark green to green-black to black, brown (rare).

Crystal System:

Monoclinic

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 mineral silvialite 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 from Longido 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).

Crystal System:

Monoclinic

Class (H-M):

2/m - Prismatic

Cell Parameters:

a = 9.762(6) Å, b = 17.994(12) Å, c = 5.325(6) Å
β = 105.10(8)°

Ratio:

a:b:c = 0.543 : 1 : 0.296

Unit Cell V:

903.08 ų (Calculated from Unit Cell)

Morphology:

Prismatic crystals, reaction rims on other minerals.

Twinning:

single or multiple parallel to {100}

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ID	Species	Reference	Link	Year	Locality	Pressure (GPa)	Temp (K)
0006297	Tschermakite	Abdu Y A, Hawthorne F C (2009) Crystal structure and Mossbauer spectroscopy of tschermakite from the ruby locality at Fiskenaesset, Greenland The Canadian Mineralogist 47 917-926		2009	Fiskenaesset, Greenland	0	293

CIF Raw Data - click here to close

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.