A. Benisek

D. Bersani

E. Lambruschi

G.D. Gatta

I. Aliatis

L. Mantovani

M. Tribaudino

M.A. Carpenter

P.P. Lottici

AIR Universita degli studi di Milano

PERIODICO di MINERALOGIA
established in 1930
PERIODICO di MINERALOGIA
established in 1930
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 September, 2015 1-208  September, 2015 1-208
An International Journal of
MINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY, ORE DEPOSITS, 
PETROLOGY, VOLCANOLOGY
and applied topics on Environment, Archaeometry and Cultural Heritage
ISSN 0369-8963
 
8   European Conference on
Mineralogy and Spectroscopy
Rome, Italy, September 9-11, 2015
Edited by
Giovanni B. Andreozzi and Ferdinando Bosi
Proceedings of the 
9788868123857_436_TFB_3
th
Periodico di Mineralogia,  ECMS 2015, 17-18      
 
 
 
 
Characterization of plagioclase solid solution by Raman  
spectroscopy: a procedure for the determination  
of the chemical composition 
 
Irene Aliatis1*, Erica Lambruschi1, Luciana Mantovani1, Artur Benisek2, Danilo Bersani1,  
Michael A. Carpenter3; Diego G. Gatta4, Mario Tribaudino1 and Pier Paolo Lottici1 
 
1 Università di Parma, Dipartimento di Fisica e Scienze della Terra, Parco Area delle Scienze 7/A, 43124 
Parma, Italy 
2 Universitaet Salzburg, Materialforschung und Physik, Hellbrunnerstr. 34, 5020 Salzburg, Austria 
3 University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, UK 
4 Università degli Studi di Milano, Dipart. di Scienze della Terra, Via Botticelli 23, 20133 Milano, IT 
* Corresponding author: irene.aliatis@difest.unipr.it 
 
Plagioclases are framework silicates occurring in planetary crusts: on Earth they are the 
most common rock-forming minerals of igneous, metamorphic and sedimentary rocks, the 
most abundant minerals on the Moon and widespread in basaltic rocks on Mars and in asteroids 
like Vesta. Plagioclases are involved in several key reactions of petrologic interest, as igneous 
and metamorphic reactions. Plagioclases can be described as a solid solution ranging from the 
Na-endmember, albite (NaAlSi3O8), to the Ca-endmember, anorthite (CaAl2Si2O8), in which 
the Si:Al ratio varies.  
The investigation of their chemical composition is a key-point to understand the petrologic 
evolution of the parent rocks. EDS or WDS chemical analyses or laser ablation are common 
techniques used to get information about plagioclase composition. They require the preparation 
of the sample and are time-consuming and expensive.  
In this work, we propose Raman spectroscopy as a procedure to gain chemical information 
from plagioclases. A similar approach has already been applied to different classes of minerals 
as garnets, amphiboles and serpentine group. Unlike the aforementioned minerals, the major 
problem in plagioclases is their mixing behaviour which is complicated by the various compo-
sitional-driven phase transitions and by the Al,Si ordering. Over most of the compositional 
range, plagioclases have the collapsed  structure with no Al,Si order (i.e. the high albite 
structure), whereas on the anorthite-rich side the solid solution has the  structure due to the 
increasing tendency to Al,Si ordering. The complete order with strictly alternating Al,Si is 
achieved only in pure anorthite.  
The most comprehensive Raman investigation on feldspars (Freeman et al., 2008) led to a 
classification of the major structural types without a detailed study of the changes of the Ra-
man features within the plagioclase composition. We performed Raman investigation on a se-
ries of well characterized plagioclases, previously analysed by powder-XRD, TEM, IR spec-
troscopy and calorimetry (Carpenter et al., 1985; Tribaudino et al., 2010; Atkinson et al., 1999; 
18  Periodico di Mineralogia, ECMS 2015, 17-18 I. Aliatis et al. 
 
Benisek et al., 2013). The samples consist of 20 homogeneous purified natural, low structural 
state plagioclases, showing the highest degree of Al,Si order possible for each composition. 
The chemical composition ranges from An0 to An100. 
The difference in Raman wavenumber between the two major peaks (Ia and Ib) of the plagi-
oclases is here proposed to be indicative of their composition in terms of An composition. 
From Fig. 1 (left side), where Ia and Ib differences are plotted vs. the An content, it is possible 
to directly read the composition for the An-rich terms (An > 60%). In order to obtain composi-
tional information for Ab-rich plagioclases too, we need to plot Ia and Ib differences vs. the lin-
ewidth of the most intense Raman mode w(Ia), as shown in Fig. 1 (right side). We point out 
that the dependence of the composition from the linewidth can be obtained only for ordered 
plagioclases. For that reason, the composition of disordered Ab-rich plagioclases cannot be 
correctly obtained with this method. Both methods have been tested on three different miner-
alogical case studies: plagioclase crystals found in Juvinas eucrite meteorite, anorthite crystals 
into a CAI inclusion within the Renazzo carbonaceous chondrite meteorite, and plagioclase 
crystals with heterogeneous chemical composition from the Marsili volcano. The “Raman 
chemical compositions” suggested by our methods are in good agreement with the chemical 
analyses for plagioclase samples with An content > 60 mol%. The methods fail for disordered 
albite-rich samples where the contribution to the linewidth by the disorder is unknown.  
 
Fig. 1: Wavenumber differences Ia-Ib versus the An content (left side) and versus the linewidth of the 
most intense Raman mode w(Ia) (right side). Coloured squares refer to the case studies. 
 
References 
Atkinson A.J., Carpenter M.A. and Salje E.K.H. (1999) - Hard mode infrared spectroscopy of 
plagioclase feldspars. European Journal of Mineralogy, 11, 7-21. 
Benisek A., Dachs E. and Carpenter M.A. (2013) - Heat capacity and entropy of low structural 
state plagioclases. Physics and Chemistry of Minerals 40, 167-173. 
Carpenter M.A., McConnell J.D.C and Navrotsky A. (1985) - Enthalpies of ordering in the 
plagioclase feldspar solid solution. Geochimica et Cosmochimica Acta, 49, 947-966.  
Freeman J.J., Wang A., Kuebler K.E., Jollif B.L. and Haskin L.A. (2008) - Characterization of 
natural feldspars by Raman spectroscopy for future planetary exploration. Canadian Mine-
ralogist, 46, 1477-1500. 
Tribaudino M., Angel R. J., Camara F., Nestola F., Pasqual D. and Margiolaki I. (2010) - 
Thermal expansion of plagioclase feldspars. Contributions to Mineralogy Petrology, 160, 
899-908. 
  
Periodico di Mineralogia,  ECMS 2015, 107-108      
 
 
 
 
 
High pressure Raman spectroscopy on Ca-clinopyroxenes 
 
Erica Lambruschi1,*, Irene Aliatis1, Luciana Mantovani1, Mario Tribaudino1, Danilo Bersani1, 
Gunther Redhammer2, Giacomo Diego Gatta3 and Pier Paolo Lottici1 
 
1 Università di Parma, Dipartimento di Fisica e Scienze della Terra, Parco Area delle Scienze 7/A, 43124 
Parma, Italy 
2 Universitaet Salzburg, Materialforschung und Physik, Hellbrunnerstr. 34, 5020 Salzburg, Austria 
3 Università degli Studi di Milano, Dipartimento di Scienze della Terra, Via Botticelli 23, 20133 Milano, 
Italy 
* Corresponding author: erica.lambruschi@difest.unipr.it 
 
 
Ca-rich clinopyroxenes are considered as major constituents of the Earth mantle. For this rea-
son, they are the subject of several experiments aimed to describe their thermal and compres-
sional behaviors in order to model the elastic properties of the mantle. However, little is known 
about the pressure-induced changes in the Raman spectra of Ca-rich clinopyroxenes. Ca-
clinopyroxenes have monoclinic symmetry (space group C2/c). The general formula of pyrox-
enes is M2M1T2O6, where M2, M1, and T are cations hosted respectively in a distorted eight-
fold-coordinated polyhedron (M2), in a regular octahedron (M1), and in a tetrahedron (T); the 
anion is invariably oxygen. 
The samples of this study have formula Ca2+M1T2O6, where M1 is populated by Mg2+ or Co2+, 
and the T site by Ge4+ or Si4+. They are all synthetic (Mantovani et al., 2015), except for Si di-
opside (Prencipe et al., 2000). An ETH-type diamond anvil cell (DAC) was used for the high-
pressure experiments. The crystalline samples (100 x 60 x 50 μm) were placed in the gasket 
hole along with some ruby chips for pressure measurements by the ruby-fluorescence method 
(precision ±0.05 GPa). Methanol:ethanol = 4:1 mixture was used as hydrostatic pressure-
transmitting medium (Angel et al., 2007). Room and high-pressure Raman spectra were col-
lected in compression up to 7.6 GPa for silicates and to 8.27 GPa for germanates, respectively, 
using an Olympus BX40 microscope attached to a Jobin-Yvon Horiba LabRam confocal Ra-
man spectrometer. The samples were excited with the 473.1 nm blue light of a doubled 
Nd:YAG laser. The spectra were collected in backscattering geometry in the spectral range 
100-1000 cm-1. Every measurement of the ruby fluorescence was calibrated using the emission 
lines of a spectroscopic zinc-vapour lamp. The positions of the fluorescence and Raman bands 
were obtained from a Gauss-Lorentzian deconvolution procedure with the LabSpec v. 5 soft-
ware, with an uncertainty of about 1 cm-1.  
The high-pressure Raman experiments showed no phase transition within the P-ranges investi-
gated, as all the peak positions vary linearly as a function of pressure. Our data confirm the 
previous experimental findings on Si-diopside (Chopelas et al., 2000). In all the investigated 
108  Periodico di Mineralogia, ECMS 2015, 107-108 E. Lambruschi et al. 
 
 
samples, all the Raman peaks shift upon compression, but the major changes in wavenumber 
are attributed to the bending and stretching modes of the tetrahedral chains (i.e., the building 
units of the pyroxene structure) (Figure 1). Upon compression, the kinking angle between tet-
rahedra decreases and the wavenumber of the bending mode increases (Lambruschi et al., 
2015). Among the samples, Ge-pyroxenes show the higher P-induced peak-position shifts, be-
ing more compressible than corresponding silicates. 
 
FIGURE 1: Raman shifts for selected bands vs. pressure for CaMgSi2O6, CaMgGe2O6, CaCoSi2O6, 
CaCoGe2O6. Lines are the fits through the data-points: their slopes Δν/ΔP are given. 
 
References 
Angel R. J., Bujak M., Gatta G.D., Jacobsen S.D. (2007) - Effective hydrostatic limits of pres-
sure media for high-pressure crystallographic studies. Journal of Applied Crystallographie, 
40, 26-32. 
Chopelas A., Serghiou G. (2002) - Spectroscopic evidence for pressure-induced phase transi-
tions in diopside. Physics and Chemistry of Minerals, 29, 403 – 408. 
Lambruschi E., Aliatis I., Mantovani L., Tribaudino M., Bersani D., Redhammer G. J., Lottici 
P. P. (2015) - Raman spectroscopy of CaM2+Ge2O6 (M2+=Mg, Mn, Fe, Co, Ni, Zn) clinopy-
roxenes. Journal of Raman Spectroscopy, DOI 10.1002/jrs.4681. 
Mantovani L., Tribaudino M., Aliatis I., Lambruschi E., Lottici P. P., Bersani D. Raman spec-
troscopy of CaCoSi2O6–Co2Si2O6 clinopyroxenes (2015) - Physics and Chemistry of Min-
erals, 42, 179-189.  
Prencipe M., Tribaudino M., Pavese A., Hoser A., Reehuis M. (2000) - A single-crystal neu-
tron-diffraction investigation of diopside at 10 K. Canadian Mineralogist, 38, 183-189. 
 


Characterization of plagioclase solid solution by Raman spectroscopy : a procedure for the determination of the chemical composition

ALIATIS, Irene

LAMBRUSCHI, Erica

MANTOVANI, Luciana

BERSANI, Danilo

TRIBAUDINO, Mario

LOTTICI, Pier Paolo

Benisek, A.

Carpenter, M. A.

Gatta, D. G.

Archivio istituzionale della Ricerca -  Università degli Studi di Parma

Characterization of plagioclase solid solution by Raman spectroscopy: a procedure for the determination of the chemical composition

https://air.unimi.it/retrieve/handle/2434/315587/438649/ECMS-2015_Rome.pdf

Characterization of plagioclase solid solution by Raman spectroscopy : a procedure for the determination of the chemical composition

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