Ferro-magnesian silicate

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).

Photograph 10-4 Thin section of >125-pm fraction of raw feed showing twinned feldspar (left) surrounded by fine- to medium-crystalline limestone, with ferro-magnesian silicate (hornblende) on right. (S A6872)... 

Fe and Mg react with (SiO ) to yield an isomorphic series of Fe, Mg (SiO ). These are the first formed ferro-magnesian (mafic) silicates. Later, the (SiO )" polymerize and combine selectively with above cations and other ions in magma such as K" , Na, as well as with early formed minerals to form a complex array of mafic silicates. 

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