[ FAQs ] [ Overview ] [ Missions ] [ Current brassboard ] [ Instrument ] [ Applications ]
A Raman study of olivine
A crucial task of Mars surface science is to determine past environmental
conditions, especially aqueous environments. Olivine, a basaltic mineral, is
easily altered by aqueous solutions and its alteration assemblages may be
specific to conditions of alteration . Raman spectra are produced by
molecular vibrations and provide direct means for studying the alteration
Our purpose is to:
1) Find spectral indicators of olivine alteration useful for in-situ analyses
2) Study the so called "iddingsite" mineral assemblage.
3) Determine structural and chemical variability of iddingsite components
with respect to the degree of alteration.
QBV_Olivine samples from Lunar
Crater volcanic field, NV
||QBV is a basalt cobble from a Quaternary flow at Lunar
Crater Volcanic Field, Nevada. It is vesicular and porphyritic, and its
olivine grains altered to iddingsite along their edges and fractures. The
data are from 3 traverses across iddingsite in one large olivine
phenocryst using Raman spectroscopic point counts, supplemented with EMP
Mineral phases found in altered olivine
||Mineral phases identified:
1). original olivine
2). altered olivine
3). polymerized silicates
6). no saponite was found
|Raman linear traverses were taken across the
original and alteration zone in olivine grains
Raman spectral indication of olivine
|Both Raman peaks of the olivine doublet
(820 and 850 cm-1) broaden and weaken in proximity to the iddingsite while
peak positions shift upwards.
||Good olivine spectra indicate Mg/(Mg+Fe) =
0.6 at the rim of the phenocryst and 0.55 in the unaltered core [6-8]. The
820 cm-1 peak position shifts upward more than the 850 cm-1 peak. When
plotted relative to each other, the points fall outside the normal range
Polymerized silicates as alteration
|Comparing with silicates of different
polymerization, the spectra of “polymerized” silicates imply a
structure whose degree of polymerization lies between that of a
double-chain and sheet silicate. Typical phyllosilicates have
presumably not yet formed. The breadth of the peaks imply that it is
||Fig.5 implies variable degrees of
polymerization or a mixture of polymerized structures.
Fig.6 demonstrates that the polymerized phase is
developing at the expense of the olivine structure.
|Electron microprobe analyses indicate
removal of Si and Mg from zones of alteration that cannot be attributed
solely to igneous zonation. Although olivine compositions are consistent
with incipient hydration, progressive alteration to lower SiO2
and MgO and higher FeO is not consistent with simple hydration and
dilution. Iddingsite compositions lie on trajectories that depart from
Fo-Fa mixing lines and the FeO trajectory projects to goethite.
Reference: Kuebler K. E., Wang A., Haskin L. A., Jolliff B. L., A
Study of Olivine Alteration to Iddingsite Using Raman Spectroscopy. Abstract
#1953, 34th LPSc, 2003.
[ 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 ]