[ FAQs ] [ Overview ] [ Missions ] [ Current brassboard ] [ Instrument ] [ Applications ]
Structure & Chemistry of
The pyroxene mineral group is of particular interest in planetary sciences. Determining
the compositional and structural characteristics of pyroxenes in rocks can be crucial to
understanding their petrogenesis. In this study, we evaluate the feasibility to determine
both structure and composition of quadrilateral pyroxene [(Mg,Fe,Ca)Si2O6]
using only Raman spectra as would be obtained from on-surface planetary measurements. Such
characterization would also be useful in terrestrial field and laboratory investigations.
The studied samples include 5 lunar rocks, 2 Martian meteorites, and 7 sets of terrestrial
rocks and minerals grains.
A. CharacteristicRaman spectra of pyroxene
|The detail features in Raman spectral patterns
can be used to distinguish among different structures of quadrilateral pyroxene.
||Raman spectral peak positions are the key to
determining pyroxene cation mole fractions. Note the deconvolved peaks in spectrum a.
||Correlations are shown among the positions of
three Raman peaks and the molar ratios of the three principal cations in pyroxene
octahedral sites. Histograms indicate the number of cases as a function of parameter
B. Determination of pyroxene cation mole fraction using Raman data
|Predicted values of cation molar ratios
Mg/(Mg+Fe+Ca) and Ca/(Mg+Fe+Ca) obtained by Raman measurements are compared with
EMP-determined values for basaltic pyroxenes in a Martian meterite and in the lunar rock
used to calibrate the Raman peak positions. The lower graphs show the absolute values of
discrepancies between Raman and EMP values. Note the large
percent errors for Ca2+ mole fraction at values <0.08. These erroneous
values are all overestimates and can be detected and corrected because the structural
pattern of the spectra allows their identification as low-Ca orthopyroxene.
||Predicted values obtained from Raman measurements are
compared with EMP-determined values of cation mole fraction for equilibrated pyroxenes in
two lunar rocks and five terrestrial samples. Errors for Mg2+ cation fraction
are of the same magnitude as for basaltic pyroxenes (~0.1). The larger errors for both
low-Ca orthopyroxene and hedenbergitic high-Ca pyroxenes can be detected from the
structural patterns and corrections made.
C. Distinguish basaltic pyroxene, equilibrated pyroxene, and non-quadrilateral
|Raman spectra of several non-quadrilateral pyroxenes
||Frequency distributions of peaks in the 300-400 cm-1
region (peak 3) obtained by point-counting Raman experiments are shown for pyroxenes from
different rock types.
References: Wang A., Jolliff B. L., Viskupic K. M.,
Haskin L. A., “Raman spectroscopic characterization of different types of
pyroxene”, Abstracts of Papers Submitted to the Twenty-eighth Lunar and
Planetary Science Conference, Part 3, P1491-1492, 1997.
A., Jolliff B. L., Haskin A. L., Kuebler E. K., "Raman spectral features of
pyroxene - Application to Martian meteorites Zagami & EETA79001", Thirty Lunar
and Planetary Science Conference, (1999) Huston, Texas, USA.
A., Haskin L. A., Jolliff B. L., Kuebler, K.E., Characterization of structure
and compositions of quadrilateral pyroxenes by Raman spectroscopy --
implication for future planetary exploration, 31th LPSc, 2000.
Wang A., Jolliff B. L., Haskin L. A., Kuebler K. E., Viskupic
K. M., (2001), Characterization and comparison of structural and compositional
features of planetary quadrilateral pyroxenes by Raman spectroscopy, American
Mineralogists. V86, p790-806.
[ lunar_sample ] [ point_count ] [ zagami ] [ akb ] [ oxides1 ] [ calib_rock ] [ grain_size ] [ mojave_rocks ] [ cored_samples ] [ sulf_carbonates ] [ sa chert ] [ pyroxene ] [ phyllosilicate ] [ ocean clays ] [ los Angeles ] [ fido2001 rocks ] [ eeta79001 ] [ alba_spores ] [ lichen ] [ earth_life ] [ oxides2 ] [ feldspar ] [ alt_olivine ]