Assertion: pure silicon | /r/AtLocation | practically all rocks
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Source sentences:
text: Pure silicon is too reactive to be found in nature, but it is found in practically all rocks as well as in sand, clays, and soils, combined either with oxygen as silica (SiO 2 , silicon dioxide) or with oxygen and other elements (e.g., aluminum, magnesium, calcium, sodium, potassium, or iron) as silicates.