Pyroxene minerals

Jade, which has been valued in carving by eastern Asians for centuries, is generally one of two minerals—pyroxene or jadeite (NaAl(Si03)2) and the amphibole nephrite, Ca2(Fe+ )5 and/or Ca2(Mg+ )5(Si40n)2(0H)2. X-ray diffraction has shown the presence of triple chains in nephrite. 

Walsh, D., Donnay, G. Donnay, J. D. H. (1974) Jahn-Teller effects in ferro-magnesian minerals pyroxenes and olivines. Bull. Soc. Franc. Mineral. Cristallogr., 97, 170-83. 

Similar relationships are found for other elements like Sc and Cr. In the sand-sized fractions, the REE distribution patterns show a more pronounced negative Eu anomaly and higher La/Lu ratio for the material from Unit N as compared to samples from Unit B. Interpretation of these observations is difficult because the heavy fractions contain as many as 10 different minerals. Pyroxene (mainly augite), amphiboles (mainly hornblende), iron oxides, chromite, ilmenite, rutile, and zircon were identified by using a polarizing microscope and energy-dispersive X-ray analysis. However, the... 

Compositions of the pervasive layered deposits seen in Mars Global Surveyor imagery (Malin and Edgett, 2000) have not been measured directly. However, TES spectra, which are dominated by sand-sized particles, indicate that igneous minerals (pyroxenes and plagioclase) are abundant on the martian surface. Quartz, which should be readily detectable in TES spectra, has not been observed. Deconvolutions of the spectra of soils and dust are dominated by framework silicates, either plagioclase or zeolites (Bandfield and Smith, 2003 McSween et aL, 2003). 

Silicates—Compounds made primarily of silicon and oxygen. Two examples are the minerals pyroxene and olivine. 

Longhi et al. 1999) and amphibolite (Christensen Mooney 1995 Rudnick Fountain 1995). For any of these compositions, partial melting and extraction of the anorthosite suite had to result in a general increase of restitic minerals (pyroxene and garnet). The occurrence of this process at a large scale, as the volume of mid-Proterozoic meta-anorthosites would require, would have produced a restitic bulk composition of the lower crust and a decrease of VpjVs ratios to values inconsistent with our observations. 

Fig. 13. 52 Two layers in the Forrestal Range that are composed of cumulates of oxide minerals, pyroxene, and plagioclase have high concentrations of vanadium of 2,000 ppm. The basal pyroxenite + oxide layer also contains elevated concentrations of cobalt, nickel and Ti02, but sulfur, copper, and chromium in the basal layer are not enriched (Appendix 13.6.9). In general, the concentrations of metals in the rocks of the Forrestal Range do not correlate with the modal concentrations of pyroxene and oxide minerals in contrast to the Dufek Massif (e.g.. Fig. 13.49) (Data from Ford et al. 1983)...

Mineral pyroxenes occur at compositions of the type MSi03, and these structures are characterized by the presence of chains of Si04 tetrahedra, joined at two corners. 

FIGURE 14.38 The basic structural unit of the minerals called pyroxenes. Each tetrahedron is an SiC)4 unit (like that in structure 11), and a shared corner represents a shared O atom (red in the inset where one O atom lies directly over an Si atom). The two unshared O atoms each carry a negative charge. 

Brantley, S. L. and Chen, Y. (1995). Chemical weathering rates of pyroxenes and amphiboles. In Chemical Weathering Rates of Silicate Minerals" (A. F. White and S. L. Brantley, eds), Mineralogical Society of America Washington, EXT, Reviews in Mineralogy 31,119-172. 

In zone (1), quartz, K-feldspar, epidote, chlorite, prehnite and sphene are predominant alteration minerals. Epidote, prehnite and carbonate replace plagioclase phenocryst. Epidote often occurs as a veinlet with several millimeters wide, together with prehnite. K-feldspar, calcite and quartz tend to occur as a veinlet. Chlorite replaces pyroxene... 

The collection of spectra obtained at Spirit s landing site reveals various miner-alogical signs of weathering. Spectra obtained on the basaltic rocks and soil on the plains show mainly olivine and pyroxene and small amounts of nonstoichio-metric magnetite, and only comparably small amounts of weathering. An example... 

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...

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