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Unformatted text preview: Crystallography In any detailed study we would have to consider the crystallography of the rocks in detail as this gives insights into where and how they were formed. That is a different course, but we can illustrate some general principles with some simple examples. Thus, for example, we can look at the basic Silica Tetrahedron: This has Silicon and Oxygen ions - Si 4+ , O 2-- and so is overall (SiO 4 ) 4- . In Olivines this silicate tetrahedron is found with Mg and Fe fitting between the tetrahedra. This gives aween the tetrahedra. This gives a very compact structure. In Pyroxenes we have the (Si 2 O 6 ) 4- grouping with two oxygen atoms shared between two tetrahedra - this gives chains of tetrahedra. In Feldspars e.g KAl(Si 3 O 8 ) we have groups of 2 double-tetrahedra (Si 4 O 8 ) with one Si replaced by Al. We can classify types of rock, as distinct from minerals, by i) density or ii) fabric. With density we would get quartz and feldspars as low density and pyroxenes and olivines as high density -...
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.
- Fall '10