Inosilicates

Inosilicates - 1 III- Inosilicates A- Pyroxene Group...

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1 III- Inosilicates A- Pyroxene Group Composition and structure : XYZ 2 O 6 X: occupied by Na, Ca, Fe, Mg, Mn, or Li. Also known as the M2 site. C.N. = 8 (in clinopyroxenes) or 6 (in orthopyroxenes). Y: occupied by Fe, Mg, Mn, Fe 3+ , Al, Cr or Ti. Also known as the M1 site. C.N. = 6. The M2 site is larger, and although in orthopyroxenes, both sites are occupied by Fe Types of pyroxenes : Orthopyroxenes : with the space group Pbca and a structure shown in Fig. 1. Clinopyroxenes 1 /c which applies to the low Ca clinoyroxenes (pigeonite; Fig. 4). Compositional variations, types and relations: The Pyroxene quadrilateral (Fig. 5). Sodic pyroxenes (Fig. 6). Incomplete solid solution between ortho- and clinopyroxenes: (Fig. 7) maximum amount of CaO in an Opx is 5 wt% (usually < 1.5 wt%). Optical properties: (Fig. 8; Table 1) Colorless to pale colors in thin section, weakly pleochroic, cleavage: excellent to v. good in 2 directions: {110} and {1 1 0}; 90° (Fig. 3); high relief, n > b, strong birefringence, extinction angles variable, but overall large (close to 45°; Fig. 8; Table 1), n and δ generally increase with increasing Fe/Mg, most members biaxial positive. Occurrence:
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This note was uploaded on 02/27/2012 for the course GLY 314 taught by Professor Staff during the Spring '09 term at Marshall.

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Inosilicates - 1 III- Inosilicates A- Pyroxene Group...

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