Olivine, magnesian

Reactions 4 and 5. Bohlen and Boettcher (1981) studied the effect of the presence of magnesian and manganoan terms in the mixture on the distribution of ferrous component between orthopyroxene and olivine according to the reaction... 

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). 

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. 

Fig. 93. Equilibrium of magnesian-iron minerals in rocks with excess silica. A. In silicate iron-formations (aqueous fluid. Cum + Px -t- OH- Q association). B. In carbonate iron-rich rocks (carbonic acid fluid. Car -(- Px -I- 01 -t- Q association). Figures indicate maximum iron content of orthopyroxene in association with quartz and olivine.

O Hara, M.J., 1963. Distribution of iron between coexisting olivines and calcium-poor pyroxenes in peridotites, gabbros, and other magnesian environments. Am. J. Sci., 261 32-46. 

The Iherzolitic shergottites are magnesian (Mg —70) olivine - clinopy roxene - chromite cumulates, dominated by coarse-grained poikilitic pigeonite enclosing rounded olivine (and chromite) crystals, with interstitial areas... 

Radomsky P. M. and Hewins R. H. (1990) Formation conditions of pyroxene-olivine and magnesian olivine chondmles. Geochim. Cosmochim. Acta 54, 3475-3490. 

Figure 3 Effects upon olivine phase equilibria near 410 km depth of low temperatures in subduction zones, for mineral thermodynamic parameters of Fei et al. (1991). Dark lines denote boundaries of subducting slab. Phases are (a) olivine, (P) wadsleyite, (-y) ringwoodite, (mw) magnesiowustite, and (pv) ferro-magnesian silicate perovskite. Note that the a — 3 transition near 410 km is first uplifted and then bifurcates into a strongly uplifted diffuse a — a + -y transition overlying a weakly uplifted sharp boundary (after Bina, 2002) (vertical resolution is 1 km).

Falloon T. J. and Green D. H. (1986) Glass inclusions in magnesian olivine phenocrysts from Tonga evidence for highly refractory parental magmas in the Tongan arc. Earth Planet. Set Lett. 81, 95-103. 

Fig. 3. Three possible mechanisms that could allow the segregation and accumulation near the surface of the Earth of highly magnesian olivine and orthopyroxene.

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