Olivines synthetic

A similar synthetic strategy was applied in the synthesis of menogaril 83, another important anthracycline antitumour antibiotic, and to the synthesis of the tricyclic core of olivin 87, the aglycon of the antitumour antibiotic olivomycin [61,62]. In both cases a tandem benzannulation/Friedel-Crafts cyclisation sequence yielded the tetracyclic and tricyclic carbon core, respectively (Scheme 42). 

Geologists have found that the mineral quartzite as well as synthetic quartz is softened by water (Griggs and Blacic, 1965). Dry quartz crystals retain then-hardnesses to nearly 1000 °C, but are weakened considerably (nearly an order of magnitude) by the presence of water. Similar weakening is observed for olivine (Mg,Fe)2(Si04) and feldspar (KAlSi3Os). 

Mossbauer spectra have been measured for various tektites, as well as for both natural and synthetic iron-bearing silicate minerals. These results are reported and compared with other similar studies available in the literature. The ratios of the intensities of the appropriate Mossbauer lines have been used to determine the ferric-ferrous ratios where possible. The spectra of the ferrosilite-enstatite series of pyroxenes show four lines which are interpreted as two quadrupole split doublets, and the ratio of the intensities of these lines indicates the degree of ordering in filling the available metal ion sites. Similar studies on the fayalite-forsterite series of olivines are also reported. 

Bish D. L. (1981). Cation ordering in synthetic and natural Ni-Mg olivine. Amer. Mineral, 66 770-776. 

Finnerty T. A. (1977). Exchange of Mn, Ca, Mg and A1 between synthetic garnet, orthopyroxene, clinopyroxene and olivine. Carnegie Inst. Wash. Yb., 68 290-292. 

Leeman W. P. and Lindstrom D. J. (1978). Patritioning of Ni + between basaltic and synthetic melts and olivines—an experimental study. Geochim. Cosmochim. Acta, 42 801-816. 

Matsui Y. and Nishizawa O. (1974). Iron magnesium exchange equilibrium between coexisting synthetic olivine and orthopyroxene. Amer. Jour. Set, 267 945-968. 

Matsui Y. and Syono Y. (1968). Unit cell dimension of some synthetic olivine group solid solutions. Geochem. Jour, 2 51-59. 

Although Cr2+ ions are rare and unstable in terrestrial minerals, their presence is suspected in olivines and pyroxenes from the Earth s Mantle and the Moon (Bums, 1975a Smith, 1971). Crystal field spectra exist for these silicates, as well as other synthetic Cr2+-bearing phases, and parameters are summarized in table 5.12. Just one spin-allowed transition, corresponding to 5Eg - 5T2g, might... 

Variations of extinction coefficients and spectrum profiles with changes in chemical composition of a mineral provide information on cation ordering in the structure. Examples involving Al3+-Mn3+ ordering in epidotes and andalusites are discussed in 4.4.2 and 4.5, and Mn2+-Fe2+ ordering in olivine is illustrated in fig. 4.8. Compositional variations of intensities of absorption bands in polarized spectra of orthopyroxenes described in 5.5.4. (fig. 5.15) have yielded Fe2+/M2 site populations (Goldman and Rossman, 1979), while similar trends in the crystal field spectra of synthetic Mg-Ni olivines described in 5.4.2.4 (fig. 5.12) have yielded site occupancy ratios of Ni2+ ions in the olivineMl and M2 sites (Hu etal., 1990). 

The strong enrichment of Ni2+ ions in the smaller Ml sites in liebenbergite (Bish, 1981) has been confirmed for a variety of synthetic Mg2+-Ni2+ and Fe2+-Ni2+ olivines by X-ray structure refinements (Rajamani et al., 1975 Bish, 1981 Bostrom, 1987 Ottonello et al., 1989), Mossbauer spectroscopy (Annersten etal., 1982 Nord etal., 1982 Ribbe and Lumpkin, 1984),CHEXE (Taftp and Spence, 1982 Smyth and Taft0, 1982) and crystal field spectral measurements (Hu et al., 1990) described in 5.4.2.4. 

The X-ray structure refinement of a synthetic Mg-Co2+ olivine (Ghose and Wan, 1974 Ghose et al., 1975) show that Co2+ ions also favour the Ml sites. The Xddata plotted in fig. 6.3 indicate that cobalt is less strongly enriched than Ni2+ ions in the Ml sites. The X-ray structure refinements (Ghose et al., 1975) and Kd data plotted in fig. 6.3 show that Zn2+ ions also favour the olivine Ml sites. 

The relative enrichments of divalent cations in the orthopyroxene Ml or M2 sites are demonstrated by the intersite Xddata plotted in fig. 6.3. Most of the divalent transition elements have Kd values less than one, indicating that they favour the larger, more distorted M2 sites. In contrast, Ni2+ ions are enriched in the smaller Ml sites of synthetic Mg2+-Ni2+ orthopyroxene (Ghose et al., 1975), having a Kd value of about two. Note that the relative enrichment of Ni2+ ions in the orthopyroxene M1 sites is not as strong as it is in the olivine M1 sites. 

Forbes, 1983), show that Cr3+ and Fe3+ ions preferentially populate the slightly larger A12 sites corresponding to the mirror plane acentric M2 sites of the olivine structure. The EPR measurements indicated that 78 per cent of the Cr3+ ions in a synthetic alexandrite occur in the A12 positions. This contrasts with the slight enrichment of Cr3+ in the Ml sites of forsterite (Rager, 1977). 

Similarly, the synthetic liebenbergite (Ni051Mgo49)2Si04, in which site populations in the olivine structure were estimated to be (Bostrom, 1987 Ottonello et al., 1989)... 

This calculation shows that the formation of intermediate liebenbergite by mixing of Mg2Si04 and Ni2Si04 components is accompanied by an excess CFSE of mixing of -5.65 kJ/mole. These results suggest that Mg2+-Ni2+ olivines depart considerably from ideal solution behaviour (Bish, 1981). This is further demonstrated in fig. 7.4 by the compositional variation of excess CFSE of mixing for the suite of synthetic Mg2+-Ni2+ olivines for which site occupancy and CFSE data are available (table 7.2). 

Bostrom, D. (1987) Single-crystal X-ray diffraction studies of synthetic Ni-Mg olivine solid solutions. Amer. Mineral., 72,965-72. 

McCormick, T. C., Smyth, J. R. Lofgren, G. E. (1987) Site occupancies of minor elements in synthetic olivines as determined by channeling-enhanced X-ray emission. Phys. Chem. Minerals, 14, 368-72. 

Nord, A. G., Annersten, H. Filippidis, A. (1982) The cation distribution in synthetic Mg-Fe-Ni olivines. Amer. Mineral., 67,1206-11. 

The materials most commonly used as gems and ornamental stones are listed in Table 2.9. This is by no means a complete listing of all materials ever used in jewelry or for decorative purposes. There are many worked specimens that are one-of-a-kind, made from unexpected materials that were opportunistically obtained. These often pose problems of identification and consequently of conservation, since once a stone has been worked it loses its natural luster and form. Stones have been altered with dyes and heat for thousands of years, so it does not hold true that just because something is in an old artifact or Grandma s necklace that it cannot be dyed or otherwise not natural. Synthetics are relatively new, but imitations are as old as the stones themselves. If someone wanted a red gem, and there were no rubies available, then a garnet or spinel could be used instead. No emeralds Use an olivine (peridot) or green sapphire. A synthetic must have the same composition and internal structure as the natural material, but an imitation just has to look like the natural stone. 

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