Sodium Through Argon
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Feldspars are silicates in which one fourth to one half of the Si4+ ions in the tetrahedra have been replaced by Al3+, thereby requiring one additional +1 charge from a positive ion for each such substitution. Since feldspars are open, three-dimensional cage structures, they are lighter than pyroxenes and olivine. In the original stratification of the planet, feldspars floated to the top, and today make up 60% of the crust of the Earth by weight. Quartz, which also is light, is responsible for another 12%. Micas and clays contribute 5%, the heavier pyroxenes 12%, and dense olivine only 3% of the crust, with the last 8% being iron oxides and miscellaneous minerals. Granite, probably the most familiar of all rocks, is a mixture of fine crystals of quartz, feldspar, and mica. It is interesting to reflect that all of this silicate geology
arose because silicon cannot make double bonds with oxygen. |
If by some cosmic readjustment, the size of a silicon atom were to decrease by 25 %, then such a double bond would become possible. All of the silicates in our planet would boil away in clouds of SiO2, gas, leaving behind only a metallic core of half the present radius, covered by a scum of metal oxides. It is easy to see why the "fitness of the worId" was used by theologians of the past century as a scientific demonstration of the existence of a Designer in the universe. The "fitness" of carbon and silicon for the separate roles they play on our planet is uncanny. |
