Pyroxenes spectra

Fig. 8.33 Left, robotic arm with MIMOS II positioned on the rock Adirondack, as seen by the navigation camera of the rover Right. Mossbauer Spectrum (14.4 keV temperature range 220-280 K) of the rock Adirondack at Spirit landing side Gusev Crater, plains. The data were taken at the as-is dusty surface (not yet brushed). The spectrum shows an olivine-basalt composition, typical for soil and rocks in Gusev plains, consisting of the minerals olivine, pyroxene, an Fe doublet, and nonstoichiometric magnetite...

Present M sbauer Studies of Natural Pyroxenes and Olivines. Table IX gives the major element chemical compositions of the silicate minerals examined in this study. Table X compares the Mossbauer parameters of these minerals, while Figures 9-13 show representative Mossbauer spectra. Fayalite (Figure 9) is the only olivine in this group. The two lines are, however, somewhat broadened (0.35 and 0.39 mm./ sec.) compared with the width of natural iron foil lines observed with our source (0.24 mm./sec.) and suggest the near coincidence of two quadrupole-split doublets resulting from Mi and M2 sites. Analysis of this "two-line spectrum into a four-line spectrum in the manner described by Evans et al (11) could possibly yield parameters for the two iron sites, but this was not undertaken since both lines appear symmetric. The "two-line quadrupole splitting of 2.78 mm./sec. is somewhat smaller... 

Mossbauer spectrum of ferrosilite-enstatite series of pyroxenes... 

O-Donor ligands. The pyroxene NaTiSi206, synthesized at high pressure (65 kbar) and temperature (1550 °C), is obtained as light-green crystals when quenched to room temperature. A-Ray studies showed that the crystals are of the NaM SijOg structural type, and the diffuse reflectance electronic spectrum confirmed that this is one of the few oxides known to contain Ti . ... 

Spectra of comet Hale-Bopp, showing features attributable to silicate minerals, (a) Profile of fine structure in the 10 silicate emission feature a peak at 11.2 and a shoulder at 11.9 are due to olivine, and a slope change at 9.2 results from pyroxene, (b) Expanded infrared spectrum exhibiting a number of sharp peaks due to magnesian olivine and pyroxene. The region of (a) is bounded by a small box. Modified from Crovisier et al. (2000) and Hanner and Bradley (2003). 

Figure 10.1 Comparisons of visible to near-infrared spectra of calcic pyroxene in transmitted and reflected light. Polarized absorption spectra of single crystals are correlated with the reflectance spectrum of a powdered sample of the same mineral (cf. fig. 5.14).

The contrasting temperature-induced shifts of the pyroxene 1 and 2 pm bands could lead to erroneous estimates of the composition and, to a lesser extent, structure-type of a pyroxene-bearing mineral assemblage deduced from the remote-sensed reflectance spectrum of a hot or cold planetary surface if room-temperature determinative curves, such as that shown in fig. 10.5, are used uncritically. For example, remote-sensed spectra of planets with hot surfaces, such as Mercury and the Moon, would lead to overestimates of Fe2+ contents of the orthopyroxenes and underestimated Fe2+ contents of the clinopyroxenes (Singer and Roush, 1985). Planets with cold surfaces, such as Mars and the asteroids, could produce opposite results. On the other hand, the room-temperature data underlying the pyroxene determinative curve shown in fig. 10.5 may impose constraints on the compositions of pyroxenes deduced from telescopic spectra of a planet with very high surface temperatures, such as Mercury. 

Already the first infrared observations of late-type giant stars have revealed that many of them are indeed surrounded by thick dust shells (Woolf Ney 1969). These were rapidly found to consist of carbonaceous dust (some kind of soot) if the stellar spectrum indicates the star to be carbon-rich, and to be silicate dust (olivine, pyroxene) if the star is oxygen-rich (Gilman 1969). Since this dust is mixed into the interstellar medium due to mass loss by stellar winds, it was then assumed that silicate and carbon particles are abundant dust components in the interstellar medium. 

Fig. 20.30 Rock sample image recorded with a digital camera. In the red circle, the region wet with Ag colloid is highlighted. The micro-SERS spectrum is compared with the normal Raman spectrum of a pyroxene single crystal. Exciting line 785 nm...

Fig. 20.32 Microscopic image of a pyroxene rock wet with a micro-RNA solution and then with Ag colloid. The micro-SERS spectrum of micro-RNA is shown below. Exciting line 785 run...

The first Mossbauer spectrum recorded on the surface of Mars was obtained in the Columbia Hills of Gusev Crater [83] close to the Rover landing site (Fig. 2.48). It clearly revealed Fe containing species (olivine and pyroxene) as well as some Fe species, not yet identified at that stage. The discovery of olivine, commonly found in lava on earth, was quite informative since this mineral is known to weather to clays and iron oxides in the presence of water [84, 85]. 

The many Mossbauer investigations of the spectra taken by the MERs on soils and rocks along their pathways showed olivines and pyroxenes as the main silicates [294—296]. Most interesting was the obvious observation of a jarosite spectrum, inferring the former presence of water on Mars [297]. This was also corroborated by the identification of goethite in the spectra from some locations [298]. 

Figure 9 Resonant absorption spectrum of Fe (295 K) in lunar soil from the Apollo 11 landing site at Mare Tranquillitatis. The absorption in the range between 0 and 0.3 mm s results primarily from iron in silicate glass, pyroxene and olivine the peaks at lower and higher velocities are due to metallic iron.

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