Silicon Dioxide Origin on Earth
Country: United States
Date: August 28, 2005
How is sand, SiO2 formed in the earth?
what depth, temperature and pressure?
I already know that sand is made
by breaking large rocks into small. What I really want to know is what
are the temperature and pressure deep in the earth that make silicon, a
mostly unreactive element, react with oxygen to make Si02.
You have made an assumption that SiO2 (and presumably other numerous
silicate minerals) were formed from the elements during the formation of
the Earth. That is not the case. In fact, elemental silicon is not found
anywhere in the Earth's crust. Neither is elemental O2 found in any
appreciable amounts in the Earth's crust.
Chemical analysis of the Moon, Mars, asteroids and comets also indicate
that silicon is present as various silicate minerals. Geological models
suggest that silicates being less dense than other compounds forming the
mantle and core of the Earth rose to the surface of the early periods of
the Earth's formation accounting for its abundance in the Earth's crust and
its relative scarcity deep within the Earth. Also your statement that
silicon is "mostly unreactive" is not accurate. If finely divided into a
powder it reacts readily with oxygen and halogens. The latter also react
readily with water to form SiO2 and the halogen acid so one does not find
silicon halides except in lab conditions.
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