Disilicates_Ring_Silicates

Disilicates_Ring_Silicates - Disilicates and Ring Silicates...

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Unformatted text preview: Disilicates and Ring Silicates Disilicates Not a common group of minerals (i.e. not rock forming) widely distributed most common ones are epidote group:- epidote- zoisite- clinozoisite- allanite Characteristic features- Pair of silica tetrahedrons - share single O- Si/O ratio = 2/7 Structure essentially edge sharing Al octahedron- octahedron are linked by double silica tetrahedron- also linked by other cations Epidote group - Structure- one edge sharing octahedral chain: M2 sites- second edge sharing octahedral chain: M1 site with Al, M3 site with other cations (usually Fe and Mn)- chains and cross linked tetrahedron produce 7 to 11 fold coordination sites A sites- commonly contain Ca five sites: tetrahedron, 3 octahedron (M1, M2, and M3), and one high coordination 1 number A site chains are parallel to b axis cleavage is commonly between chains (along b axis) Composition: A site M3 site Epidote Ca Al, Fe Clinozoisite Ca Al Allanite Ca, Ce, La, Na...
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Disilicates_Ring_Silicates - Disilicates and Ring Silicates...

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