• A very hard mineral composed of silica, SiO<sub>2</sub>, found worldwide in many different types of rocks, including sandstone and granite. Varieties of quartz include agate, chalcedony, chert, flint, opal, and rock crystal.
  • The common form of native silica, Or the oxid of silicon (SiO<sub>2</sub>).
  • A form of silica, or silicon dioxide (SiO2), occurring in hexagonal crystals, which are commonly colorless and transparent, but sometimes also yellow, brown, purple, green, and of other colors; also in cryptocrystalline massive forms varying in color and degree of transparency, being sometimes opaque.
  • The most abundant <xref>mineral</xref> on the earth's surface, of chemical composition <xref>silicon dioxide</xref>, <xref>Si</xref><xref>O</xref>2. It occurs in a variety of forms, both <xref>crystalline</xref> and <xref>amorphous</xref>. Found in every environment.
  • colorless glass made of almost pure silica
  • a hard glossy mineral consisting of silicon dioxide in crystal form; present in most rocks (especially sandstone and granite); yellow sand is quartz with iron oxide impurities
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