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Tweddillite from
Prabornaz Mine (Praborna Mine), Saint-Marcel, Aosta Valley, Italy

Locality type:Mine
Classification
Species:Tweddillite
Formula:{CaSr}{Mn3+AlMn3+}(Si2O7)(SiO4)O(OH)
Chemical Analyses:
Oxide wt%:
12
SiO232.6 %33.0 %
ThO20.2 %0.2 %
Al2O312.9 %13.6 %
Ga2O30.1 % %
Cr2O30.1 % %
La2O39.2 %3.1 %
Ce2O30.2 %0.3 %
Pr2O31.5 %0.8 %
Nd2O32.6 %1.9 %
Sm2O30.1 %0.1 %
Mn2O315.0 %19.4 %
Fe2O31.5 %1.2 %
MnO1.4 %0.9 %
MgO2.2 %0.6 %
CaO10.6 %13.7 %
SrO7.2 %8.6 %
Na2O0.5 %0.2 %
H2O1.6 %1.7 %
Total:99.5 %99.3 %
Sample references:
SampleReference
1pt. 23Frank K. Mazdab collection, thin section FKM-171 (https://www.rockptx.com/fkm-151-to-fkm-175/#FKM-171)
2pt. 34  "  "
Comments:For normalized analyses of tweddillite and piemontite from this locality, as well as data for accompanying minerals in the examined thin section, see:
https://www.rockptx.com/fkm-151-to-fkm-175/#FKM-171

In my instructional YouTube video tutorial on "Normalizing epidote-group minerals in MS Excel" (https://www.youtube.com/watch?v=IbMLngyz4Cs), the Prabornaz mine "piemontite" analysis I used to illustrate the normalization calculations turned out to be a REE-bearing tweddillite (named as "manganipiemontite-(Sr)" based on the Armbruster et al., 2006 nomenclature).

The sample for this thin section was collected by Pilar Lecumberri-Sanchez (Univ. Arizona) on a field trip to the locality.
Colour:in thin section, pleochroic in yellow, orange, red and magenta; similar to and essentially indistinguishable from other Mn-rich members of the epidote group.
Confirmation
Validity:Believed Valid
References
References:Frank K. Mazdab collection (see https://www.rockptx.com/fkm-151-to-fkm-175/#FKM-171 for normalized analysis)
Data
Mineral Data:Click here to view Tweddillite data
Locality Data:Click here to view Prabornaz Mine (Praborna Mine), Saint-Marcel, Aosta Valley, Italy
 
Mineral and/or Locality  
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