Editing 2501: Average Familiarity
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Minerals like feldspars and olivine generally exist as a continuum of varying chemical formulas, represented as a mixture of "endmembers" that have some pure composition. Feldspars are a category of aluminum-containing silicate minerals that account for the most of the rock in the earth's crust by mass. They are composed of a silicon-aluminum-oxygen lattice filled with sodium, potassium, or calcium ions. The major varieties are CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub> (anorthite), NaAlSi<sub>3</sub>O<sub>8</sub> (albite), and KAlSi<sub>3</sub>O<sub>8</sub> (potassium feldspar). Olivine is most notable as being the primary constituent of the upper mantle and commonly found in stony meteorites, and has the formula X<sup>2+</sup><sub>2</sub>SiO<sub>4</sub>, where X is any iron or magnesium ion. The ends of the spectrum are Mg<sub>2</sub>SiO<sub>4</sub> ({{w|forsterite}}) and Fe<sub>2</sub>SiO<sub>4</sub> ({{w|fayalite}}). | Minerals like feldspars and olivine generally exist as a continuum of varying chemical formulas, represented as a mixture of "endmembers" that have some pure composition. Feldspars are a category of aluminum-containing silicate minerals that account for the most of the rock in the earth's crust by mass. They are composed of a silicon-aluminum-oxygen lattice filled with sodium, potassium, or calcium ions. The major varieties are CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub> (anorthite), NaAlSi<sub>3</sub>O<sub>8</sub> (albite), and KAlSi<sub>3</sub>O<sub>8</sub> (potassium feldspar). Olivine is most notable as being the primary constituent of the upper mantle and commonly found in stony meteorites, and has the formula X<sup>2+</sup><sub>2</sub>SiO<sub>4</sub>, where X is any iron or magnesium ion. The ends of the spectrum are Mg<sub>2</sub>SiO<sub>4</sub> ({{w|forsterite}}) and Fe<sub>2</sub>SiO<sub>4</sub> ({{w|fayalite}}). | ||
β | In the title text the two geologists express belief that the average person ''should'' be more familiar with silicates because of how ubiquitous they are. Their somewhat-exasperated statement plays on the phrase "you can't throw a rock without hitting one," a standard hyperbole about how common something is. Indeed, {{w|Silicate mineral|silicate}} rocks are extremely common on Earth — not only would a rock thrown in a random direction stand a decent chance of striking a silicate mineral rock | + | In the title text the two geologists express belief that the average person ''should'' be more familiar with silicates because of how ubiquitous they are. Their somewhat-exasperated statement plays on the phrase "you can't throw a rock without hitting one," a standard hyperbole about how common something is. Indeed, {{w|Silicate mineral|silicate}} rocks are extremely common on Earth — not only would a rock thrown in a random direction stand a decent chance of striking a silicate mineral rock but the randomly-selected rock being ''thrown'' also has a very high chance of being a silicate mineral rock. With the exception of a few carbonate deposits, rocks found in large deposits on Earth's surface nearly all have silica in them, even extraterrestrial rocks. The Earth's crust is about 60% silica by weight.<ref>"Constraining crustal silica on ancient Earth" C. Brenhin Keller, T. Mark Harrison. ''Proceedings of the National Academy of Sciences'' Sep 2020, 117 (35) 21101-21107; DOI: 10.1073/pnas.2009431117</ref> |
==Transcript== | ==Transcript== |