One member of this crystal's namesake group with cubic structure is called cristobalite. Its interweaving with moganite produces chalcedony, and this material undergoes conchoidal fracture. Stishovite or its shocked form is found an impact craters. It has the lowest crystallization temperature on Bowen's reaction series. Pure crystals of this substance exhibit the piezoelectric effect. For 10 points, identify this mineral formed from tetrahedral of silicon dioxide, which has a value of 7 on the 
One member of this crystal's namesake group with cubic structure is called cristobalite. Its interweaving with moganite produces chalcedony, and this material undergoes conchoidal fracture. Stishovite or its shocked form is found an impact craters. It has the lowest crystallization temperature on Bowen's reaction series. Pure crystals of this substance exhibit the piezoelectric effect. For 10 points, identify this mineral formed from tetrahedral of silicon dioxide, which has a value of 7 on the Mohs scale and whose varieties include "rose," flint, and amethyst.
One member of this crystal's namesake group with cubic structure is called cristobalite.
quartz [accept SiO2 before silicon dioxide]