Quartz

Chemical name |  Silicon dioxide
Chemical formula |  SiO2
Identification
Colors |  Clear (with no impurities)
Crystal habit |  6-sided prism ending in 6-sided pyramid
Crystal system |  rhombohedral
Cleavage |  None
Fracture |  Conchoidal
Hardness |  7
Name origin |  German "Quarz".
Specific gravity |  2.65
Streak |  White

Quartz is the second most common mineral found on Earth being the primary component of sand. More accurately known as silicon dioxide, quartz has a chemical composition of SiO2 arranged in a repeating lattice forming hexagonal crystals. Pure quartz is clear, but colored variations are created because of impurities in the crystal. Quartz is number 7 on the Mohs Hardness Scale.
Quartz is used in a number of applications; most commonly in glass making but also abrasives, electrical components or decorative gemstones especially if colored by impurities.